11th International Workshop on Positron and Positronium Chemistry (PPC‐11) Book of Abstracts Cidade de Goa, Goa, INDIA November 9‐14, 2014 11th International Workshop on Positron and Positronium Chemistry (PPC‐11) International Scientific Committee
A. Alam
C. Q. He
T. Hirade
Y. C. Jean
Y. Kobayashi
J. Kuriplach
F. H. J. Maurer Chair
Y. Nagashima
P. K. Pujari
K. Ratzke
D. M. Schrader Emeritus
S. V. Stepanov
UK
China
Japan
USA
Japan
Czech Republic
Sweden
Japan
India
Germany
USA
Russia
Advisory Committee
R. K. Sinha, Chairman, Atomic Energy Commission, India
S. Basu, Director, BARC, Mumbai
P. R. Vasudeva Rao, Director, IGCAR, Kalpakkam
K. L. Ramakumar, Director, RC&I Group, BARC, Mumbai
D. Srivastava, Director, VECC, Kolkata
M. K. Sanyal, Director, SINP, Kolkata
S. K. Aggarwal, Asso. Director, RC&I Group, BARC, Mumbai
B. N. Jagatap, Director, Chemistry Group, BARC, Mumbai
S. R. Shetye,Vice Chancellor, Goa University, Goa
C. S. Sundar, Director, Materials Group, IGCAR, Kalpakkam
S. L. Chaplot, Director, Physics Group, BARC, Mumbai
S. G. Markandeya, Controller, BARC, Mumbai
N. Ramamoorthy, Asso. Director, IC&TC, BARC, Mumbai
Organized
by
Bhabha Atomic Research Centre
11th International Workshop on Positron and Positronium Chemistry (PPC‐11) Organizing Committee
Local Organizing Committee
A. Goswami, RCD, BARC
Chair
P. K. Pujari, RCD, BARC
Convener
A. V. R. Reddy, ACD, BARC
B. S. Tomar, RACD, BARC
P. Singh, IADD, BARC
G. K. Dey, MSD, BARC
M. G. R. Rajan, RMC, BARC
D. Srivastava, MSD, BARC
S. K. Gupta, TPD, BARC
S. K. Gupta, IADD, BARC
I. Samajdar, IIT, Mumbai
C. Ranganathaiah, University of Mysore
V. Ravindrachary, Mangalore University
Y. K. Vijay, University of Rajasthan
G. Amarendra, IGCAR
B. Ganguly, SINP
P. M. G. Nambissan, SINP
M. Patri, NMRL
A.V. Salker, Goa University
K. Madangopal, GAMD, BARC
C. S. Bal, AIIMS
K. Sivaji, University of Madras
P.K. Pujari, BARC
Chair
R. Acharya, BARC
Suparna Sodaye, BARC
K. Sudarshan, BARC
Secretary
R. Tripathi, BARC
D. Dutta, BARC
S. K. Sharma, BARC
Priya Maheshwari, BARC
S. Mukherjee, BARC
S.K. Rath, NMRL
Co-organized by
Indian Association of Nuclear Chemists and Allied Scientists Saha Institute
of Nuclear Physics Indira Gandhi Centre for Atomic Research 11th International Workshop on Positron and Positronium Chemistry Technical Program
Sunday
November 9, 2014
15:30
Registration and Fellowship
19:00
Dinner
Monday
November 10, 2014
9:00-10:00
Inauguration
10:00-10:30
In Memoriam
10:30-11:00
Tea Break
11:00-13:00
Technical Session I : Polymer/Nanocomposite/Membrane
11:00-11:35
PL1
Nanoparticle filled polymers: Dispersion, Interactions and Free
Volume
Frans H. J. Maurer
11:35-12:00
IT1
Aging and Free Volume in Thin Polymer Membranes
K. Rätzke
12:00-12:12
OP1
Accounting for lack of “Nano-effect” in a thermoset/clay
nanocomposite: A positron annihilation study
S. K. Rath
12:12-12:24
OP2
Carborane-siloxane polymers and cross-linked hybrid elastomers
studied by Positron Annihilation Lifetime Spectroscopy and
Differential scanning Calorimetry.
D. Hughes
12:24-12:36
OP3
Gas transport and free volume study in polyethylene based
membranes
Pushkar N. Patil
12:36-12:48
OP4
The effect of UV irradiation on per-fluorinated sulfonic acid/PTFE
copolymer studied by positron annihilation
Hamdy F. M. Mohamed
13:00-14:00
Lunch
14:00-15:30
Technical Session II : Fundamental
14:00-14:35
PL2
Early intratrack processes initiated by fast positrons and Augerelectrons
S. V. Stepanov
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry 14:35-15:00
IT2
Understanding the enigmas of Positron/Positronium chemistry
B. N. Ganguly
15:00-15:12
OP5
High-precision calculation of loosely bound states of LiPs+ and
NaPs+
T. Yamashita
15:12-15:24
OP6
Kinetic energy of Ps formed by Ore mechanism in Ar gas
Y. Sano
15:30-16:00
Tea Break
16:00-17:30
Technical Session III : Nanomaterials and Alloys
16:00-16:25
IT3
Nuclear material studies by positron annihilation spectroscopy
Y. Nagai
16:25-16:45
IP1
Positron Annihilation Spectroscopy and TEM studies on Zr base
alloys used for nuclear reactor application
D. Srivastava
16:45-16:57
OP7
Effect of yttria nanoparticles on steels for nuclear applications
I. Bartošová
16:57-17:09
OP8
Positron annihilation spectroscopy of dilute Uranium based alloys
S. Mukherjee
17:09-17:21
OP9
The investigation of implanted alloys using positron annihilation
spectroscopy with combination of nanoindentation technique
V. Sabelová
17:21-17:31
New products and technologies in radiation measurements
Paul Davidson
19:00
Cultural program and Dinner
Tuesday
November 11, 2014
9:00-10:30
Technical Session IV : Metals and Semiconductors
9:00-9:35
PL3
Theoretical positron and positronium studies of condensed matter
and their relation to experiment
J. Kuriplach
9:35-10:00
IT4
Characterization of thin transparent metal-oxide semiconductors
Rafael Ferragut
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry 10:00-10:12
OP10
Effect of alkali metal ions in vacancy defect and defect cluster in
MgO nanocrystallites by positron annihilation spectroscopy
S. Selvakumar
10:12-10:24
OP11
Study of positron systematics in Li irradiated Alumina (α-Al2O3)
P. V. Gaikwad
10:24-10:36
OP12
Unmanageable defects in proton-irradiated silicon: a factual
outlook for positron probing
N. Yu. Arutyunov
10:36-11:00
Tea Break
11:00-13:00
Technical Session V: Fundamentals
11:00-11:25
IT5
Optical Preparation and Manipulation of Positronium Atoms
D. B. Cassidy
11:25-11:50
IT6
Ps Spin conversion reaction during Ps-Xe collisions
K. Shibuya
11:50-12:02
OP13
Wave packet dynamics of vibrational Feshbach Resonances in
positron scattering from fluoromethane
J. R. Mohallem
12:02-12:14
OP14
H  Production from collisions between positronium and keV
antiprotons for GBAR
P. –A. Hervieux
12:14-12:26
OP15
Precise measurement of energy spectrum of orthopositronium
decay
S. Adachi
12:26-12:36
New products and technologies in radiation measurements
C. Sudeesh
12:36-12:46
Instruments for measurement of ionizing radiation
P. C. Swain
13:00-14:00
Lunch
14:00-16:00
Technical Session VI : Liquids/Confinement
14:00-14:25
IT7
Silica gel loaded with ionic liquids studied by positron annihilation
techniques
C. Hugenschmidt
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry 14:25-14:50
IT8
N-heptane adsorption and desorption in mesoporous materials
monitored in situ by positron annihilation lifetime spectroscopy
R. Zaleski
14:50-15:10
IP2
Phase behaviour of water confined in nanodomain
Priya Maheshwari
15:10-15:30
IP3
Positronium bubble oscillation in room temperature ionic liquids
T. Hirade
15:30-15:42
OP16
Positron annihilation in benzene, aniline and cyclohexane
K. Fedus
15:42-15:54
OP17
Manifestation of the tunnelling effect in positronium and muonium
liquid-phase reactions
P. S. Stepanov
16:00-16:30
16:30-19:30
Tea Break
Technical Session VII : Poster Presentation
19:30
Wednesday
Dinner
November 12, 2014
9:00-10:30
Technical Session VIII : Polymers/Nanocomposites
9:00-9:35
PL4
Free volume, molecular mobility and polymer structure – an
outline of some practical applications
M. Ashraf Alam
9:35-9:55
IP4
Characterization of interfaces in binary and ternary polymer blends
by Positron Lifetime Spectroscopy
C. Ranganathaiah
9:55-10:07
OP18
PLT and DBAR investigations on MPDMAPP doped PVA-PVP
blend
R. F. Bhajantri
10:07-10:19
OP19
Physical selectivity of molecularly imprinted polymers evaluated
through free volume size distributions derived from Positron
Lifetime Spectroscopy
T. Pasang
10:19-10:31
OP20
Investigation of PCM microcapsules at low temperature and high
pressure by PALS method
B. Zgardzińska
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry 10:31-11:00
Tea Break
11:00-13:00
Technical Session IX : Surfaces, Interfaces and Polymer Blends
11:00-11:25
IT9
Positron surface processes
Yasuyuki Nagashima
11:25-11:50
IT10
Total-reflection high-energy positron diffraction (TRHEPD)
T. Hyodo
11:50-12:10
IT11
Depth profiles and free volume in aircraft primer films
J. D. Van Horn
12:10-12:22
OP21
Direct correlation between free volume and dielectric constant in a
fluorine-containing polyimde blend
R. Ramani
12:22-12:34
OP22
PALS and DBAR study on LiClO4 doped PVA - NaAlg blend
based polymer electrolyte
T. Sheela
12:34-12:44
Absolute method for estimation of beta activity
K. R. Kasyapa
13:00
Lunch & Excursion
Thursday
November 13, 2014
9:00-10:30
Technical Session X: Nanomaterials, Metallic and Non-metallic Solids
9:00-9:35
PL5
Understanding materials behaviour: Role of Positron annihilation
Spectroscopy
C. S. Sundar
9:35-9:55
IP5
Positron annihilation spectroscopic studies
Bi1-xPrxFeO3 nanocrystalline compounds
P. M. G. Nambissan
9:55-10:07
OP23
Temperature dependent positron annihilation characterization of Fe
based and other superconductors
D. Sanyal
10:07-10:19
OP24
Investigation on the oxygenation effect of porous silicon from the
EMD by Positron Annihilation
K. Sivaji
Cidade de Goa, Goa, India November 9­14, 2014 of
multiferroic
11th International Workshop on Positron and Positronium Chemistry 10:19-10:31
OP25
Positron annihilation spectroscopy of Eu and Dy doped α’-Sr2SiO4:
Understanding difference in their local site occupancy
S. K. Gupta
10:31-10:43
OP26
Vacancy structure in niobium monoxide ceramics by meansof
PALS, DBS spectroscopy and QM calculations
A. A. Valeeva
10:43-11:00
Tea Break
11:00-13:00
Technical Session XI : Soft matter, Liquids and Defects
11:00-11:25
IT12
Depth resolved positron beam studies of defect in graphite
G. Amarendra
11:25-11:50
IT13
Application of localized annihilation of positron and o-Ps
Y. Honda
11:50-12:10
IP6
Positronium chemistry in liquids - first investigations at the GiPS
setup
M. Butterling
12:10-12:22
OP27
Effect of local electric field on the Positronium formation in
irradiated polymer
V. Ravindrachary
12:22-12:34
OP28
Electron beam induced microstructural changes and electrical
conductivity in Bakelite polymer RPC detector material -A
positron lifetime study
K. V. Aneesh Kumar
12:34-12:46
OP29
Positron Annihilation Spectroscopy on LiBH4 and LiBH4:LiI
superionic lithium conductors
Morten Eldrup
12:46-12:58
OP30
Investigation on correlation between defects and conductivity of
Sb-doped SnO2 thin films
W. Mao
13:00-14:00
Lunch
14:00-15:30
Technical Session XII : Biological Applications
14:00-14:25
IT14
The potential of newer PET radiopharmaceuticals in enhancing the
scientific basis of clinical practice
S. Basu
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry 14:25-14:50
IT15
Nanostructural characterization of complex carbohydrate polymers:
Recent progress
M. Roussenova
14:50-15:02
OP31
Novel applications of PALS in biophysics and cancer research
E. Axpe
15:02-15:14
OP32
Positron studies in biopolymer composites
A. Coveney
15:14-15:26
OP33
A study of synthetic and natural dyes by the positron annihilation
lifetime spectroscopy
A. Pivtsaev
15:30-16:00
Tea Break
16:00-17:30
Technical Session XIII: Porous Material
16:00-16:25
IT16
Ps cooling in silica-based porous materials
R. S. Brusa
16:25-16:50
IT17
Positronium annihilation in mesoporous silica thin films
Chunqing He
16:50-17:15
IT18
Positron annihilation study in metal organic framework
D. Dutta
17:15-17:27
OP34
Examination of a coal by means of positron annihilation
spectroscopy
C. A. Palacio
17:27-17:39
OP35
Bose-Einstein condensation of positronium in silica pores
O. Morandi
17:39-17:51
OP36
Cesium loading capacity of iron phosphate glasses studied by
positron annihilation spectroscopy
S. Abhaya
19:00
Banquet
Friday
November 14, 2014
9:00-10:30
Technical Session XIV : Facilities and Experimental
9:00-9:35
PL6
The MePS System at Helmholtz-Zentrum Dresden-Rossendorf
R. Krause-Rehberg
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry 9:35-10:00
IT19
Evidence for a positron bound state on the surface of a topological
insulator and details of a new positron beam system for materials
studies under development at The University of Texas at Arlington
A. H. Weiss
10:00-10:25
IT20
AIST positron probe microanalyzer and its application
N. Oshima
10:30-11:00
11:00-12:00
Tea Break
Technical Session XV : Facilities and Experimental
11:00-11:25
IT21
Positron-Annihilation
bremsstrahlung
A. Wagner
11:25-11:37
OP37
Spin polarized low-energy positron source
V. N. Petrov
11:37-11:49
OP38
Nanoparticles based transparent ceramics for scintillation and
detection applications
F. A. Selim
12:00-13:00
Lifetime
spectroscopy
Summary Talk and Conclusion
PL: Plenary Talk IT: Invited Talk IP: Invited Presentation OP: Oral Presentation P : Poster Presentation Cidade de Goa, Goa, India November 9­14, 2014 using
electron
11th International Workshop on Positron and Positronium Chemistry Plenary Talks
PL1
Nanoparticle filled polymers: Dispersion, Interactions and Free Volume
Page
No.
2
PL2
Early intratrack processes initiated by fast positrons and Auger-electrons
3
PL3
Theoretical positron and positronium studies of condensed matter and
their relation to experiment
4
PL4
Free volume, molecular mobility and polymer structure – an outline of
some practical applications
5
PL5
Understanding materials behaviour: Role of Positron annihilation
Spectroscopy
6
PL6
The MePS System at Helmholtz-Zentrum Dresden-Rossendorf
7
Invited Talks
IT1
Aging and free volume in thin polymer membranes
9
IT2
Understanding the enigmas of positron/positronium chemistry
10
IT3
Nuclear material studies by positron annihilation spectroscopy
11
IT4
Characterization of thin transparent metal-oxide semiconductors
12
IT5
Optical preparation and manipulation of positronium atoms
13
IT6
Ps spin conversion reaction during Ps-Xe collisions
14
IT7
Silica gel loaded with ionic liquids studied by positron annihilation
techniques
15
IT8
N-heptane adsorption and desorption in mesoporous materials monitored
in situ by positron annihilation lifetime spectroscopy
16
IT9
Positron surface processes
17
IT10
Total-reflection high-energy positron diffraction (TRHEPD)
18
IT11
Depth profiles and free volume in aircraft primer films
19
IT12
Depth resolved positron beam studies of defect in graphite
20
IT13
Application of localized annihilation of positron and o-Ps
21
IT14
The potential of newer PET radiopharmaceuticals in enhancing the
22
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry scientific basis of clinical practice
IT15
Nanostructural characterization of complex carbohydrate polymers:
Recent progress
23
IT16
Ps cooling in silica-based porous materials
24
IT17
Positronium annihilation in mesoporous silica thin films
25
IT18
Positron annihilation study in metal organic framework
26
IT19
Evidence for a positron bound state on the surface of a topological
insulator and details of a new positron beam system for materials studies
under development at The University of Texas at Arlington
27
IT20
AIST positron probe microanalyzer and its application
28
IT21
Positron-Annihilation
bremsstrahlung
lifetime
spectroscopy
using
electron
29
IP1
Positron Annihilation Spectroscopy and TEM studies on Zr base alloys
used for nuclear reactor application
31
IP2
Phase behaviour of water confined in nanodomain
32
IP3
Positronium bubble oscillation in room temperature ionic liquids
33
IP4
Characterization of interfaces in binary and ternary polymer blends by
positron lifetime spectroscopy
34
IP5
Positron annihilation spectroscopic studies of multiferroic Bi1-xPrxFeO3
nanocrystalline compounds
35
IP6
Positronium chemistry in liquids - first investigations at the GiPS setup
36
IP7
A dynamical calculation method of an electron and a positron slowing
down process in liquid water
37
Invited Presentations
Oral Presentations
OP1
Accounting for lack of “Nano-effect” in a thermoset/clay nanocomposite:
A positron annihilation study
39
OP2
Carborane-siloxane polymers and cross-linked hybrid elastomers studied
by positron annihilation lifetime Spectroscopy and differential scanning
calorimetry.
40
OP3
Gas transport and free volume study in polyethylene based membranes
41
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry OP4
The effect of UV irradiation on per-fluorinated sulfonic acid/PTFE
copolymer studied by positron annihilation
42
OP5
High-precision calculation of loosely bound states of LiPs+ and NaPs+
43
OP6
Kinetic energy of Ps formed by Ore mechanism in Ar gas
44
OP7
Effect of yttria nanoparticles on steels for nuclear applications
45
OP8
Positron annihilation spectroscopy of dilute Uranium based alloys
46
OP9
The investigation of implanted alloys using positron annihilation
spectroscopy with combination of nanoindentation technique
47
OP10
Effect of alkali metal ions in vacancy defect and defect cluster in MgO
nanocrystallites by positron annihilation spectroscopy
48
OP11
Study of positron systematics in Li irradiated Alumina (α-Al2O3)
49
OP12
Unmanageable defects in proton-irradiated silicon: a factual outlook for
positron probing
50
OP13
Wave packet dynamics of vibrational feshbach resonances in positron
scattering from fluoromethane
51
OP14
H  Production from collisions between positronium and keV antiprotons
for GBAR
52
OP15
Precise measurement of energy spectrum of orthopositronium decay
53
OP16
Positron annihilation in benzene, aniline and cyclohexane
54
OP17
Manifestation of the tunnelling effect in positronium and muonium
liquid-phase reactions
55
OP18
PLT and DBAR investigations on MPDMAPP doped PVA-PVP Blend
56
OP19
Physical selectivity of molecularly imprinted polymers evaluated through
free volume size distributions derived from Positron Lifetime
Spectroscopy
57
OP20
Investigation of PCM microcapsules at low temperature and high
pressure by PALS method
58
OP21
Direct correlation between free volume and dielectric constant in a
fluorine-containing polyimde blend
59
OP22
PALS and DBAR study on LiClO4 doped PVA - NaAlg blend based
polymer electrolyte
60
OP23
Temperature dependent positron annihilation characterization of Fe based
Cidade de Goa, Goa, India November 9­14, 2014 61
11th International Workshop on Positron and Positronium Chemistry and other superconductors
OP24
Investigation on the oxygenation effect of porous silicon from the EMD
by Positron Annihilation
62
OP25
Positron annihilation spectroscopy of Eu and Dy doped α’-Sr2SiO4:
Understanding difference in their local site occupancy
63
OP26
Vacancy structure in niobium monoxide ceramics by meansof PALS,
DBS spectroscopy and QM calculations
64
OP27
Effect of local electric field on the positronium formation in irradiated
polymer
65
OP28
Electron beam induced microstructural changes and electrical
conductivity in Bakelite polymer RPC detector material -A positron
lifetime study
66
OP29
Positron Annihilation Spectroscopy on LiBH4 and LiBH4:LiI superionic
lithium conductors
67
OP30
Investigation on correlation between defects and conductivity of Sbdoped SnO2 thin films
68
OP31
Novel applications of PALS in biophysics and cancer research
69
OP32
Positron studies in biopolymer composites
70
OP33
A study of synthetic and natural dyes by the positron annihilation
lifetime spectroscopy
71
OP34
Examination of a coal by means of positron annihilation spectroscopy
72
OP35
Bose-Einstein condensation of positronium in silica pores
73
OP36
Cesium loading capacity of iron phosphate glasses studied by positron
annihilation spectroscopy
74
OP37
Spin polarized low-energy positron source
75
OP38
Nanoparticles based transparent ceramics for scintillation and detection
applications
76
OP39
When Some Elementary Free Volumes in Polymers are not seen by
Positron Annihilation Experiments
77
Poster Presentations
P1
An experiment to observe positron–atom bound states
79
P2
Nonlinear dynamics of electron–positron clusters
80
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry P3
Study of the positronium thermalization in porous materials
81
P4
Positron nitrogen molecule scattering using ro-vibrational close coupling
method
82
P5
The collision between two positronium (Ps) atoms
83
P6
The collision between positronium (Ps) and muonium (Mu)
84
P7
Positron transport in a dense structured media
85
P8
Positron annihilation characteristics in polar liquids and the firstprinciple modeling
86
P9
Study of lamellar lyotropic liquid crystalline structure by positron
lifetime spectroscopy
87
P10
PET in clinical medicine
88
P11
Positron Trapping
Nanocomposite
Photochromic
89
P12
Amorphous structure of the degraded poly(ethylene-terephthalate)
in weathering test
90
P13
DBS investigation on films of Cobalt Chloride doped PVA-PVP blend
91
P14
Computation of DBAR parameters in polypyrrole incorporated PVA
films
92
P15
Computation of size of spherical and non-spherical voids in semicrystalline polymeric materials
93
P16
Change of chemical structure, free volume, and mechanical property of
polyethylene irradiated by gamma-ray
94
P17
Influence of fillers on the structural and thermo-mechanical properties of
recycled high density polyethylene using PAS and other techniques
95
P18
Study of the structural and thermo-mechanical properties of high density
polyethylene composites using PAS and other techniques
96
P19
A free volume study on the miscibility of PEEK/PEI blend using
Positron Annihilation and Dynamic Mechanical Thermal Analysis
97
P20
Positron Annihilation
PMMA/MWNT
of
98
P21
Confined water in controlled pore glass CPG-10-120 studied by positron
annihilation lifetime spectroscopy and differential scanning calorimetry
99
Studies
on
PVA/MPDMAPP
Spectroscopy
and
orientation
Cidade de Goa, Goa, India November 9­14, 2014 study
11th International Workshop on Positron and Positronium Chemistry P22
PALS study of free voids in ion exchanged low-silica zeolites
100
P23
Characterization of contaminated clay with radioisotope using positron
annihilation spectroscopy
101
P24
Comparison study between energy-tunable positron annihilation and
flow-type ellipsometric porosimetry
102
P25
Very low energy positron scattering from W(100)
103
P26
Probing defects at the buried interfaces/layers in organic semiconductor
devices
104
P27
Metal-semiconductor interfaces investigated by positron annihilation
spectroscopy
105
P28
Development of a method to measure the positron diffusion constants in
metals by the observation of positronium negative ions
106
P29
Positron annihilation in layer high temperature superconductors
107
P30
Positron interactions with quartz materials
108
P31
Defects study on magnetic fluorescent Fe3O4/ZnSe nanocomposites by
positron annihilation spectroscopy
109
P32
Electronic properties of transition metals and alloys by positron
annihilation spectroscopy
110
P33
PAS study of Zr-2.5%Nb alloy irradiated by Ar9+ heavy ions
111
P34
Study of Doppler broadening in neutron irradiated ADS related materials
using positron annihilation spectroscopy (PAS)
112
P35
Investigation of helium implanted RAFM steel by positron beam Doppler
broadening spectroscopy
113
P36
Defect studies in large samples using Photon Induced Positron
Annihilation (PIPA) Spectroscopy
114
P37
Development of a vertical, slow positron beamline facility at AIST and
application to the study of liquids
115
P38
Design of a pulsed positron beam at Trombay
116
P39
Development of a solar spectrum monitor using coloured LEDs and
Arduino for studying celestial positronium
117
P40
A triple coincidence PALS setup based on fast pulse digitizers
118
Cidade de Goa, Goa, India November 9­14, 2014 11th International Workshop on Positron and Positronium Chemistry PLENARY TALKS Cidade de Goa, Goa, India November 9­14, 2014 1 PL 1 11th International Workshop on Positron and Positronium Chemistry Nanoparticle Filled Polymers:
Dispersion, Interactions and Free Volume*
Frans H. J. Maurer§
Department of Chemistry, Polymer & Materials Chemistry,
Lund University, Lund, Sweden
A theoretical approach, based on micromechanical and Simha’s molecular statistic
mechanical theories of the description of the appearance of interphases and their thermal
expansivities and bulk moduli in particulate filled polymers will be presented [1,2]. Some
recent free volume data measured by PALS on nanoparticle filled polymers will be reviewed.
The addition of nano-size silica particles, exfoliated clay, graphene and graphene oxide
particles dispersed in polymer matrices have a large effect on the viscoelastic properties in
the melt state as well as in the solid state.
Several questions still exist in relation to possible changes in free volume properties in
these complex systems and their characterization. In particular, results from PALS
measurements of graphene oxide filled amorphous and semi-crystalline polymers will be
presented.
[1] R. Simha, R.K. Jain, F.H.J. Maurer. Rheol. Acta 25 (1986) 161.
[2] R. Simha, E. Papazoglou, F.H.J. Maurer. Polymer Composites 10 (1989) 409.
*
Acknowledgement: National Science Foundation, Sweden.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 2 PL 2 11th International Workshop on Positron and Positronium Chemistry Early Intratrack Processes Initiated by Fast Positrons and Auger-electrons
S. V. Stepanov1,2,§, V. M. Byakov1,3, D. S. Zvezhinskiy1,2, G. Duplâtre4, Yu. D. Perfiliev5 and
L. A. Kulikov5
1
Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25,
117218, Moscow, Russia
2
National Research Nuclear University “MEPhI”, Kashirskoye shosse 31,
115409, Moscow, Russia
3
D. Mendeleyev University of Chemical Technology of Russia, Miusskaya sq., 9,
125047, Moscow, Russia
4
Institut Pluridisciplinaire Hubert Curien, CNRS/IN2P3, BP 28 67037 Strasbourg, France
5
Lomonosov Moscow State University, Chemical Department, GSP-1, Leninskie Gory,
119991, Moscow, Russia
It is well known that positrons (e+) as well as positronium atoms (Ps) are convenient
probes of the local nanoscale structure in a condensed phase and the radiolytic processes
occurring therein [1, 2]. There are several steps of evolution of a fast e+:
1) ionization slowing down, thermalization, formation of the e+ track and terminal
positron blob, effect of local heating of the e+ blob;
2) formation of the quasifree positronium and its further localization on structural
defects or formation of the Ps bubble state (in liquids). “Non-point” positronium: the pick-off
annihilation rate and shape of the Ps “narrow” component;
3) nonhomogeneous diffusion-controlled reactions in the e+ blob: Ps oxidation and
ortho-para conversion by radiolytic products, reaction rate constants, interpretation of the
PAL spectra in aqueous solutions at different temperatures.
Intratrack radiation chemical processes can be initiated not only by energetic positron
irradiation, but also by fast Auger-electrons in EMS experiments (EMS= Emission
Mössbauer Spectroscopy). The radioactive transformation of 57Co into 57Fe (E-capture by the
57
Co nucleus) is accompanied by emission of several Auger-electrons having a total kinetic
energy of about 6 keV. Their ionization slowing down leads to the formation of 200-300 ionelectron pairs (H2O+, e- in the case of aqueous solutions) around the Mössbauer 57Fe ion
(within a sphere of 100 Å radius). Such a cloud (the Auger-blob [3]) is formed within 10-13 s.
Further fast intrablob processes (ion-electron recombination, electron localization and
scavenging) can be observed experimentally by measuring the yields of final chemically
stable ions 57Fe3+ and 57Fe2+ by means of EMS. The observation of these processes is
restricted within the lifetime of the excited Mössbauer nuclei 57Fe, which is about 10-7 s. We
have studied experimentally the reaction ability of NO3- anions towards quasifree track
electrons in frozen aqueous solutions of acids and salts [3]. It was shown that NO3- scavenges
the track electron more efficiently than H3O+, but only by a factor of 3. This is in drastic
contradiction with the known behavior of nitrate ions in liquid water, where they are very
efficient electron scavenger.
[1] Y.C. Jean, P.E. Mallon, D.M. Schrader (Eds.), Positron and Positronium Chemistry,
World Scientific, Singapore, 2003.
[2] S.V. Stepanov et al., Advances in Physical Chemistry, 2012 (2012) 431962.
[3] S.V. Stepanov et al., Bulletin of the Russian Academy of Sciences. Physics series, 77(6)
(2013) 770.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 3 PL 3 11th International Workshop on Positron and Positronium Chemistry Theoretical Positron and Positronium studies of Condensed Matter
and their Relation to Experiment
J. Kuriplach§
Department of Low Temperature Physics, Charles University, Prague, Czech Republic
Positrons and positronia can probe condensed matter and bring detailed information
about studied systems via annihilation gamma-quanta. Several sophisticated experimental
techniques are available to examine such annihilation events. The role of theory is to allow
understanding of measured data and, in favorite cases, to predict quantitatively also the
results of measurements or even to forecast new phenomena. A close relationship between
theory and experiment is highly desirable in order to advance understanding of various
aspects of condensed matter which are accessible by means of positron annihilation.
In this lecture, principles of theoretical description of positron annihilation events are
briefly summarized, and several examples dealing with mainly defect studies in oxides are
discussed. It is pointed out that in some respects these theoretical/computational approaches
reached maturity, especially when the relation of the electronic structure and positron
characteristics is concerned. Persisting problems are reminded.
On the other hand, the description of positronium behavior in condensed materials is
not that developed and is substantially more complex, involving also Ps chemical aspects,
compared to positrons alone. In addition to shortly reviewing the current status of Ps
theoretical description in condensed matter, the possibilities how to unify or merge positron
and positronium theoretical concepts are discussed. Basically, there is no substantial
difference to measure the positron and positronium lifetime. Then, why it differs so much at
the theoretical level?
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 4 PL 4 11th International Workshop on Positron and Positronium Chemistry Free Volume, Molecular Mobility and Polymer Structure – An Outline of
Some Practical Applications
M. Ashraf Alam1,§, Mina Roussenova1, David Hughes1, Abigail Coveney1, P. Beavis2,
A. Swain2, Job Ubbink1, 3, Easan Sivaniah4, Concetta Tedeschi5 and
Bruno-H Leuenberger5
1
H.H. Wills Physics Laboratory, University of Bristol, Tyndall Ave. Bristol BS8 1TL, UK
2
AWE, Aldermaston, Reading, RG7 4PR, UK
3
Food Concept & Physical Design, Mühleweg 10, CH-4112 Flüh, Switzerland
4
University of Cambridge, Cavendish Laboratory, Biological and & Soft Systems Section,
Cambridge CB3 0HE, UK
5
DSM Nutritional Products Ltd, Wurmisweg 576, CH-4303 Kaiseraugst, Switzerland
It is now well established that Positron Annihilation Lifetime Spectroscopy (PALS) is a
unique and versatile technique for direct evaluation of the local free volume which exists in
polymeric matter due to their irregular molecular packing, density fluctuations and
topological constraints [1]. This local free volume, consisting of a large number of subnanometre sized free volume elements (commonly referred to as “holes”), plays an important
role in molecular mobility related phenomena such as self-diffusion, the glass transition,
mechanical strength and a host of other physical behaviour [2]. Over the past decade, PALS
has been successfully used to study a range of practical implications of the free volume in the
applications of polymers in a variety of industrial scenarios.
In this presentation, we attempt to give an overview of activities within the positron
community in recent years which aim to provide insights into the aspects of the design of
polymers for specific industrial applications with the view to attracting potential interest from
relevant industries. This talk would concentrate on relevant work of the Bristol positron
group in this area together with a summary of other similar activities within the positron
community. The talk would incorporate the following themes:
(i) free volume and barrier properties of edible biopolymers for their applications in
encapsulation of bioactive ingredients in the pharmaceutical and food industries [3],
(ii) barrier / permeation properties of appropriate polymers with the view to enable gas
permeation / separation etc. [4], and
(iii) role of free volume in polymer nano-composites [5].
[1] Y.C. Jean, P.E. Mallon and D.E. Schrader, Principles and Applications of Positron and
Positronium Chemistry (2003).
[2] G. Dlubek, in Polymer Physics: From Suspensions to Nanocomposites and Beyond, eds.
L.A. Utracki and A.M. Jamieson, John Wiley & Sons (2011).
[3] M. Roussenova et al., New J. Phys. 14 (2012) 035016.
[4] Q. Song et al., Energy & Environmental Science, 5 (2012) 8359.
[5] see for example D.J. Hughes et al., J. Phys: Conf Series, 443 (2013) 012045.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 5 PL 5 11th International Workshop on Positron and Positronium Chemistry Understanding Materials Behavior: Role of Positron Annihilation
Spectroscopy
C. S. Sundar§
J.C. Bose Fellow, Materials Science Group, Indira Gandhi Centre for Atomic Research,
Kalpakkam, India
In this talk, I shall present an overview of positron annihilation studies of defects
in materials, being pursued at IGCAR, that encompass systems of relevance to the fast
breeder reactor programme, as also investigation of defects in novel materials. Results
on the investigation of nanoprecipitates in steels aimed towards the development of
radiation resistant steels, and on Fe-phosphate glassy matrices for radioactive storage
will be presented. As an illustration of the studies on novel materials, we present results
on the evolution of pore structure with annealing temperature in nanoporous gold and
its influence on hardness, as also investigations on Se vacancies in Bi2Se3 that
influences the observation of magnetoresistance quantum oscillations in this
topological insulator. The scope of the presentation will be to illustrate as to how
positron studies, coupled with other experimental techniques can provide insight into
the behavior of traditional and exotic materials.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 6 11th International Workshop on Positron and Positronium Chemistry PL 6 The MePS System at Helmholtz-Zentrum Dresden-Rossendorf
R. Krause-Rehberg1,§, W. Anwand2, M. Butterling2, T. E. Cowan2, M. Jungmann1,
A. Müller1 and A. Wagner2
1
2
Univ. Halle, Dept. of Physics, 06099 Halle, Germany
HZDR, Institute of Radiation Physics, P.O. Box 510119, 01314 Dresden, Germany
MePS is the Mono-energetic Positron Source at ELBE (Electron LINAC for beams with
high Brilliance and low Emittance) at the HZDR (Helmholtz-Zentrum Dresden-Rossendorf).
The user operation started in 2013. The chopper was also added to the system in 2013 leading
to very clean spectra almost without any spurious signals and a peak-to-background ratio of
>104. The current time resolution of about 400 ps is expected to be further improved during
the next beam times in summer 2014. The MePS system is especially suited for the lifetime
spectroscopy of positronium. The reason is that the repetition frequency can be reduced to 26
MHz × 2-n, n=0, 1, 2 … 16. This is possible without noticeable losses in intensity in this
range. The reason is that the transported charge of individual electron bunches can be
increased until either the average beam power of > 40 kW or the maximum bunch charge of
> 77 pC is exceeded. In the moment an electron bunch repetition time of 615 ps is our
standard time setting. This is ideal for rather long o-Ps lifetimes which are to be expected in
porosimetry studies of mesoporous pore systems.
In the talk, the recent progress of the MePS system will be demonstrated. Examples for
porosimetry studies will be shown. Furthermore, planned improvements such as an MCPPMT diagnostic stage and the concept of a new sample chamber including a sample
magazine and a temperature sample stage will be introduced.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 7 11th International Workshop on Positron and Positronium Chemistry Invited Talks Cidade de Goa, Goa, India November 9­14, 2014 8 11th International Workshop on Positron and Positronium Chemistry IT 1 Aging and Free Volume in Thin Polymer Membranes
K. Rätzke1,§, S. Harms1, T. Koschine1, C. Ohrt, F. Faupel1, L. Ravelli2 and W. Egger2
1
Materials Science, University of Kiel, Kiel, Germany
2
University of Armed Forces, Munich, Gemany
Polymers are widely used nowadays, from simple plastic bags via insulating materials
to high tech applications like adhesives or gas separation membranes, and many applications
like gas separation membranes or adhesive applications require thin polymeric films on
substrates. Important for properties like diffusion, viscosity, and permeability of membranes
is the free volume, which is, to a first approach, the unoccupied space between atoms. This
free volume can be probed by positron annihilation lifetime spectroscopy, in particular, as a
simple quantum mechanical model allows semi-quantitative calculation of average hole size
from measured o-Ps lifetime.
In the present talk, selected applications of positron annihilation lifetime spectroscopy
to various problems of thin polymeric films on substrates will be presented. For high free
volume membrane materials, on the one hand, aging, i.e. decreasing of the available free
volume and thus the performance with time has to be taken into account. As an example, we
have measured the change in free volume during aging of thin films of a polymer of intrinsic
microporosity (PIM-1) by depth resolved positron annihilation lifetime spectroscopy [1]. For
films with thickness, d, smaller than 1 μm, aging is nearly complete after 3 months, whereas
for films with d > 1 μm, aging continues even after several months. Aging is thickness and
time dependent and the free volume diffuses through the film to the free surface. A recent
investigation [2] shows that this effect can be partially reduced by incorporating carbon
nanotubes without reducing membrane performance.
On the other hand, the substrate might affect the free volume due to restrictions in
alignement of polymer chains or interaction. We performed positron annihilation lifetime
spectroscopy experiments at Teflon AF/silicon interfaces as function of the positron
implantation energy to determine the free volume hole size distribution in the interfacial
region and to investigate the width of the interphase [3]. While no interphase was detected in
very short chained, solvent-free, thermally evaporated Teflon AF, an interphase of some tens
of nm in extension was observed for high molecular weight spin-coated Teflon AF films.
Recent experiments with a focussed beam through a hole in the substrate show even larger
reduction in free volume at the interface [4].
[1] S. Harms, K. Rätzke, F. Faupel, N. Chaukura, P. M. Budd W. Egger, L. Ravelli, The
Journal of Adhesion 88, (2012) 608.
[2] T. Koschine, K. Rätzke, F. Faupel, M. M. Khan, T. Emmler, V. Filiz, V.Abetz, L.
Ravelli, W. Egger, In preparation
[3] S. Harms, K. Rätzke, V. Zaporojtchenko, F. Faupel W. Egger, L. Ravelli, Polymer 52,
(2011) 505.
[4] C. Ohrt, T. Koschine, K. Rätzke, F. Faupel, N. Oshima, Y. Kobayashi, R. Suzuki, A.
Uedono, (2014) to be published.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 9 IT 2 11th International Workshop on Positron and Positronium Chemistry Understanding the Enigmas of Positron/Positronium Chemistry
Bichitra Nandi Ganguly§
Applied Nuclear Physics Division, Saha Institute of Nuclear Physics,
Kolkata, INDIA. Pin: 700064.
Positron as simplest as well as the lightest antimatter enters as the mystic world to
unravel Nature’s manifestos by simply striking the material domain and emitting 511keV
gamma line, as the resultant consequence. The marvelous discovery since (1930s), has
continued to explore the enormous phenomenological studies related to multifaceted aspects,
all of which relates to one but a vital phenomenon of its association with the various
electronic states in the matter. Accordingly, an exotic-bound state of positron–electron
(positronium) was found to exist and endowed with its annihilation characteristics, indeed
offers much to be explored in the material architecture, where its functional properties are
intimately related. This subject enlightens many interesting aspects of investigations which
will be summarized (from liquids to chemically important solid substances), the subtleties
and usefulness of the unique probe in various physico-chemical and biological systems will
be covered. Application of positron annihilation with short-lived radiotracers forming the
basis of nuclear medicine and medical diagnostics will be described briefly. Some of the
upcoming technological advances in producing many positrons and their exciting field may
be attractive and challenging to the young minds, the other field related to astrophysical
nature may still bring in more curiosity and enthusiasm, these will briefly touched. The
importance in the presentations will bring in the aspects where chemical perspective is
sought.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 10 IT 3 11th International Workshop on Positron and Positronium Chemistry Nuclear Material Studies by Positron Annihilation Spectroscopy
Y. Nagai1,§, K. Inoue1, T. Toyama1, K. Nagumo1, Y. Shimizu1, N. Ebisawa1,
M. Hasegawa1 and Y. Kobayashi1,2
1
2
Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial
Science and Technology, Umezono, Tsukuba, Ibaraki 305-8568, Japan
It is well known that positron and positronium are very useful tools to study the
degradation of the various materials related to nuclear reactors, which is very important for
the safety issues, especially after the Fukushima Dai-ichi nuclear accident. In this talk, we
will introduce the several examples to apply positron annihilation spectroscopy to the nuclear
materials.
The first topic is the neutron irradiation induced embrittlement of the reactor pressure
vessel (RPV) steels of light water reactors. The embrittlement is considered to be mainly
caused by the irradiation-induced changes in the microstructures such as the formation of the
Cu rich nano-clusters (CRNCs) and matrix damages (MDs) due to irradiation-induced point
defect clusters. The advantage to use positron annihilation, compared with other
microstructural tools such as transmission electron microscopy (TEM) and three-dimensional
atom probe (3D-AP), is that positron can detect both the MDs and the CRNCs due to positron
affinity trapping. In the presentation, we will show the applications of age-momentum
correlation (AMOC) of positron annihilation to the RPVs and their model alloy systems [1].
This technique expects to give useful information on the interaction between MD and CRNC
formations.
The second topic is the structural study on high level radioactive waste glasses (RWGs)
[2,3]. The intrinsic structural open spaces in RWGs (supposed to use silica-based glasses) are
of particular importance, because they act as stable containers to confine the radioactive
nuclei of nuclear waste for long periods. The radioactive nuclei are expected to occupy the
intrinsic structural open spaces surrounded by the glass random networks of RWGs.
Therefore, information on the structural open spaces is strongly desirable with respect to the
safe storage of radioactive nuclei. Usually, positron lifetime method (o-Ps lifetime) is
employed to estimate the size of the open spaces in glass materials using Tao-Eldrup model.
However, momentum distribution study using angular correlation of annihilation radiation
(ACAR) technique is very useful and reliable in the presence of chemical and/or spin reaction
with Ps. In the presentation, we will compare ACAR results with o-Ps lifetimes for several
model glasses of RWG, and discuss the possible interaction between Ps and the impurity
centers in the glasses.
[1] K. Inoue, Y. Nagai, Z. Tang, T. Toyama, Y. Hosoda, A. Tsuto, and M. Hasegawa, Phys.
Rev. B 83 (2011) 115459.
[2] K. Inoue, H. Kataoka, Y. Nagai, M. Hasegawa, Y. Kobayashi, J. Appl. Phys. 114 (2013)
154904.
[3] K. Inoue, H. Kataoka, Y. Nagai, M. Hasegawa, and Y. Kobayashi, J. Appl. Phys. (2014)
in press.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 11 IT 4 11th International Workshop on Positron and Positronium Chemistry Characterization of Thin Transparent Metal-Oxide Semiconductors
Rafael Ferragut§
L-NESS and Physics Department, Politecnico di Milano, Como, Italy
Istituto Nazionale di Fisica Nucleare, Milan, Italy
Most conductors are opaque and most transparent materials are insulators. However, a
small group of materials exhibit coexistence of both attributes. This effect is manifested only
in few metal-oxide thin films (ZnO, InGaZnO, TiO2 and few other). Past explanations have
largely assumed at the outset the origin of the carrier-producers (e.g. oxygen vacancies as the
source of electrons) and proceeded to explain other properties such as mobility. Recently, a
variant of growing techniques have been used to produce amorphous and crystalline
transparent thin films with an accurate thickness control. Characterization and identification
of defects in the produced films become an important task and paves the way to dominate the
nanostructural characteristics and to obtain films with good quality. In this sense, Positron
Annihilation Spectroscopy (PAS) using a variable-energy positron beam is a powerful tool.
Conventional and coincidence Doppler broadening (CDB) and positronium (Ps) fraction
measurements of thin TiO2 crystalline films, thin InGaZnO amorphous films and hybrid solar
cells based in a porous TiO2 matrix infiltrated with P3HT (poly[3-hexylthiophene]) are
presented in the present work. Vacancies in crystalline TiO2 were identified and the chemical
environment depends of the inclusion or not of Ta impurities. Based on the thickness values
of amorphous InGaZnO and porous TiO2 films which were measured accurately by means of
XRD or SEM, the film density were estimated after minimizing fits of the experimental
results with a realistic layered model (VEPFIT). Particularly, a step-change improvement in
the performance of the hybrid solar cells was enabled by engineering the hybrid interface by
the insertion of a proper molecular interlayer namely 4-mercaptopyridine (4-MP). PAS
techniques were used to monitor the effect of the interlayer on the P3HT implantation in the
porous TiO2 as a function of the molecular weight of the P3HT infiltrated. We note a
remarkable difference in terms of the positronium fraction when the 4-MP interlayer is
introduced. This difference is consistent with a better contact between the porous TiO2 and
P3HT phases and a closer polymer packing at the interface.
§
e-mail: [email protected]
web site: http://www.como.polimi.it/positron
Cidade de Goa, Goa, India November 9­14, 2014 12 11th International Workshop on Positron and Positronium Chemistry IT 5 Optical Preparation and Manipulation of Positronium Atoms*
D. B. Cassidy§
Department, of Physics and Astronomy, University College London, Gower Street, WC1E
6BT, London UK
The use of a Surko-type buffer gas trap [1] has made it possible to turn ordinary neonmoderated d.c. positron beams [2] into devices that can deliver high quality cold positrons for
high resolution scattering studies [3] or pulses containing up to 107 positrons in a ns burst [4].
The latter can be used to make a “gas” of positronium having a pressure of around 1 Torr,
which in turn can be probed with pulsed lasers in much the same way as any other atomic
species. The ability to create a Ps gas makes feasible a vast array of hitherto impractical or
impossible experiments, such as the production of molecular positronium [5]. In this talk I
will discuss some experiments in which excited atomic states of Ps can be created and
studied, including Doppler-free 2-photon state-selective production of Rydberg Ps [6] and
electrostatic manipulation thereof [7], measurement of the spin polarization of a positron
beam via optical excitation of n=2 Ps states with circularly polarized light in a magnetic field,
and the production of e+A complexes [8] via the reaction Ps *  A  e  A  e  , where the Ps* is
in an excited state chosen to have the right binding energy to maximize the reaction rate.
[1] C. M. Surko, M. Leventhal, and A. Passner, Phys. Rev. Lett. 62 (1989) 901.
[2] Positron Beams and Their Applications, edited by P. G. Coleman (World Scientific,
Singapore, 2000).
[3] S. J. Gilbert, R. G. Greaves, and C. M. Surko, Phys. Rev. Lett. 82 (1999) 5032
[4] D. B. Cassidy, S. H. M. Deng, R. G. Greaves, and A. P. Mills Jr., Rev. Sci. Instrum. 77
(2006) 073106.
[5] D. B. Cassidy, T. H. Hisakado, H. W. K. Tom, and A. P. Mills Jr., Phys. Rev. Lett. 108
(2012) 133402.
[6] T. E. Wall, D. B. Cassidy and S. D. Hogan, to be published.
[7] S. D. Hogan and F. Merkt, Phys. Rev. Lett. 100 (2008) 043001
[8] C. Harabati, V. A. Dzuba, and V. V. Flambaum, Phys. Rev. A 89 (2014) 022517.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 13 IT 6 11th International Workshop on Positron and Positronium Chemistry Ps Spin Conversion Reaction during Ps-Xe Collisions
K. Shibuya§, Y. Kawamura, and H. Saito
1
Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan
A Ps atom can undergo ortho–para spin conversion reaction during Ps–Xe collisions
due to spin–orbit interaction [1,2]. When o-Ps atoms are converted into p-Ps atoms, the
annihilation rate is considerably increased. We investigated energy–dependence of this
reaction rate and developed a new method for measuring Ps temperature.
First, we measured o-Ps annihilation rate
in gaseous Xe at several temperatures ( T , 300–
623 K) at 250 kPa using a digital-oscilloscopebased positron annihilation lifetime spectrometer.
Owing to Zeeman mixing of Ps spin states in a
magnetic field, the two-photon annihilation rate
was analytically divided into two components:
one was due to the Ps spin conversion, while the
other was due to pick-off annihilation. We found
that the spin-conversion annihilation rate was
proportional to T 2.1 , which can be explained by a
model assuming that the spin conversion occurs
only in p-wave scattering and that, Ps velocity
profile
follows
a
Maxwell-Boltzmann
distribution after thermalization (Fig. 1). We also
found that the pick-off annihilation rate was
almost proportional to T 1.0 ,which is a
dependence exceptionally stronger than that
observed in many other gases by unknown
reasons.
Second, we developed a new method
measuring Ps temperature by applying the fact
that the spin conversion annihilation rate
strongly depends on the o-Ps kinetic energy. In
other words, a small change in the energy leads
to a large change in the two-photon annihilation
rate. Utilizing the reaction as a "lens" to magnify
the o-Ps kinetic energy, we obtain its time
Fig. 1: Annihilation rates as a function of
temperature.
The
spin-conversion
annihilation rate is plotted with circles
and the pick-off annihilation rate is
plotted with triangles.
evolution by measuring the time-resolved two- Fig. 2: Time evolution of o-Ps kinetic
photon annihilation rate using an age-momentum energy. The fit curve is based on a
correlation spectrometer. The time evolution of classical model assuming elastic
collisions.
o-Ps kinetic energy can be explained by a
classical model [3] that assumes elastic collisions in a time range later than 20 ns and an
energy range of lower than 60 meV (Fig. 2). The Ps–Xe momentum-transfer cross section is
found to be 12(2) 1016 cm2.
[1] J. Mitroy and S. A. Novikov, Phys. Rev. Lett. 90 (2003) 183202.
[2] H. Saito and T. Hyodo, Phys. Rev. Lett. 97 (2006) 253402.
[3] Y. Nagashima et al., Phys. Rev. A 52 (1995) 258.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 14 IT 7 11th International Workshop on Positron and Positronium Chemistry Silica Gel Loaded with Ionic Liquids Studied by Positron Annihilation
Techniques
C. Hugenschmidt1,§, H. Ceeh1, T. Gigl1, , M. Haumann2, C. Herold1,
M. Reiner1, and A. Schönweiz2
1
Heinz Maier-Leibnitz Zentrum (MLZ) and Physik Department E21, Technische Universität
München, Garching, Germany
2
Lehrstuhl für Chemische Reaktionstechnik, Friedrich-Alexander Universität, ErlangenNürnberg, Germany
Novel materials for catalytic applications in chemical industry consist of an ionic liquid,
dispersed as a thin film on the inner surface of a highly porous solid. Dissolving
homogeneous transition metal complexes in the ionic liquid film allows tailoring of solid
materials with defined properties and a controlled chemical reactivity. These materials can be
handled like classical heterogeneous catalysts or adsorbents. Since it is of great importance to
study the film forming process in the volume of a porous support in a non-destructive manner
positron annihilation techniques have been applied.
In the present experiment we have studied silica gel samples loaded with 0-70% ionic
liquids. First, the samples were analyzed by Doppler broadening spectroscopy (DBS) and
coincident DBS. In a second step, all samples have been characterized by positron lifetime
spectroscopy (PLS) in order to observe variations of the pore size distribution. The results of
the DBS showed a very high decrease of the S-parameter of about 8% between the asreceived and the 70% loaded material. This trend is clearly supported by the CDBS
measurements. All samples show an almost linear dependence on the S- and W-parameter. In
order to get a deeper insight to the positron state in the different samples the lifetime spectra
were decomposed, and the mean void radii were determined using the Tao-Eldrup model.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 15 IT 8 11th International Workshop on Positron and Positronium Chemistry N-heptane Adsorption and Desorption in Mesoporous Materials Monitored
in situ by Positron Annihilation Lifetime Spectroscopy*
R. Zaleski1,§, M. Gorgol1, A. Błażewicz1, A. Kierys2, J. Goworek2
1
Institute of Physics, 2 Faculty of Chemistry, Maria Curie-Sklodowska University,
pl. M. Curie-Sklodowskej 3, 20-031 Lublin, Poland
The pore structure of solids is of significant importance for their numerous applications.
The most commonly used methods of pore characterization are gas adsorption experiments.
The proper interpretation of the adsorption data requires complete and precise description of
the related mechanisms (e.g., the adsorbate multilayer formation on the solid surface or
adsorbate condensation as well as pore blocking percolation and cavitation during desorption
processes). Recently positron annihilation lifetime spectroscopy (PALS) was successfully
used to investigate adsorption phenomena [1]. The in situ monitoring of n-heptane adsorption
and desorption in porous materials by PALS may give an extended insight in the mechanism
of these processes.
The intensity of the PALS component related to the mesopores is the parameter most
comparable to the results of a typical adsorption experiment. (Fig.1). However, only the
interpretation of other parameters of the PALS components, such as mean lifetime and its
dispersion, is required for better insight into the sorption process. The components related to
n-heptane inside the filled pores and silica – n-heptane interface present in the PALS spectra
reveal phenomena unknown so far. Among them is the possible reorganisation of n-heptane
molecules being in contact with the adsorbent surface when pores are filled. Moreover, the
formation of the n-heptane multilayer made of “island-like” during adsorption was observed,
while a much smoother layer of adsorbed n-heptane is present during desorption.
Fig. 1: The intensity of the mesopore-related component as a function of the n-heptane relative
pressure during adsorption (open symbols) and desorption (full symbols) for different silicas with
bell-mouthed (left), ink-bottle (middle) and cylindrical (right) pores.
[1] R. Zaleski et al., Micropor. Mesopor. Mater. 154 (2012) 142; A. Kierys et al., Micropor.
Mesopor. Mater. 179 (2013) 104; A. Kierys et al., Adsorption 19 (2013) 529.
*
The research was supported by Polish Ministry of Science and Higher Education through
the grant no. 2013/09/D/ST2/03712.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 16 IT 9 11th International Workshop on Positron and Positronium Chemistry Positron Surface Processes*
Yasuyuki Nagashima§
Department of Physics, Tokyo University of Science
1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
When low-energy positrons impinge on solid surfaces, they will penetrate into the bulk,
lose their energy until thermalized, and then diffuse back to the surface [1, 2]. The positrons
may be trapped in the surface potential well and annihilate there. If the positron work
function   is negative, the positrons may be emitted with a characteristic energy   . The
positrons may be also emitted as positronium (Ps). In the case of insulators such as SiO2, Ps
atoms are formed in the bulk.
In this presentation, I will discuss positron surface processes including (1) emission of
the positronium negative ion (Ps-) from tungsten and molybdenum surfaces [3], (2) efficient
emission of Ps- from alkali-metal coated surfaces [4,5] and (3) Ps emission from alkali-metal
coated surfaces [6]. I will also discuss about O+ emission from TiO2 induced by positron
annihilation with core electrons, which has been explored recently [7].
[1] P. Mills Jr., Positron Solid State Physics, Proceedings of the International School of
Physics “Enrico Fermi”, Course LXXXIII, North-Holland 1983, p.432.
[2] P. J. Schultz and K. G. Lynn, Rev. Mod. Phys. 60 (1988) 701.
[3] Y. Nagashima and T. Sakai, New J. Phys. 8 (2006) 319.
[4] Y. Nagashima, T. Hakodate, A. Miyamoto and K. Michishio, New J. Phys. 10 (2008)
123029.
[5] H. Terabe, K. Michishio, T. Tachibana and Y. Nagashima, New J. Phys. 14 (2012)
015003.
[6] H. Terabe, S. Iida, K. Wada, T. Hyodo, A. Yagishita and Y. Nagashima, J. Phys. Conf.
Series.
[7] T. Tachibana, T. Hirayama and Y. Nagashima, to be published in Phys. Rev. B.
*
The author is grateful for collaboration with Koji Michishio, Hiroki Terabe, Shimpei Iida,
Takashi Yamashi, Takayuki Tachibana, Izumi Mochizuki, Ken Wada and Toshio Hyodo.
This work is supported in part by a Grant-in Aid for Scientific Research (No. 24221006)
from the Ministry of Education, Science and Culture of Japan and Matsuo Foundation.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 17 11th International Workshop on Positron and Positronium Chemistry IT 10 Total-Reflection High-Energy Positron Diffraction (TRHEPD)*
T. Hyodo1,§, Y. Fukaya2, I. Mochizuki1, M. Maekawa2, K. Wada1, T. Shidara3,
A. Ichimiya4 and A. Kawasuso2
1
Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan
2
Advanced Science Research Center, JAEA, Takasaki 370-1292, Japan
3
Accelerator Laboratory, KEK, Tsukuba 305-0801, Japan
4
Dept. of Phys., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
A station for the reflection high-energy positron diffraction (RHEPD) [1,2] which is the
positron counterpart of reflection high-energy electron diffraction (RHEED) has been
installed in the Slow Positron Facility, KEK. With a high-intensity slow positron beam
(initial intensity 5×107 slow e+/s) [3] and a transmission-type brightness enhancement [4]
quality of the data obtained has been drastically improved.
Fast positrons of energy 10keV, for example, are totally reflected from a solid surface
when the incident glancing angle is less than certain critical angle, typically 2°-3°, covering
one third or one half of the whole measurement range (about 6°) of the glancing angle. This
feature, resulting from the positive average electrostatic potential in every solid, makes
RHEPD very unique compared with other diffraction methods. We have thus renamed
RHEPD as TRHEPD (total-reflection high-energy positron diffraction) to put stress on this
feature. Moreover, when the glancing angle is slightly larger than the critical angle, the
diffraction pattern includes information on the layer just beneath the surface also. By
increasing the glancing angle gradually, one can take the information of the layers of interest
without bothering about the effect of the deeper layers.
The sensitivity of TRHEPD to the atomic configuration on the topmost surface and the
immediate subsurface is demonstrated in ref. [5]. The method has been applied to determine
the one-dimensional (nano-wire) structure formed on Ge (001) when Pt atoms are deposited
[6], the buckling structure of silicene on Ag(111) [7], and the long-unresolved structure of
TiO2(110)-(1×2) surface [8].
[1] A. Ichimiya, Solid State Phenom. 28/29 (1992) 143.
[2] A. Kawasuso and S. Okada, Phys. Rev. Lett. 81 (1998) 2695.
[3] K. Wada, et al., Eur. Phys. J. D 66 (2012) 37; J. Phys.: Conf. Series 443 (2013) 012082.
[4] M. Maekawa et al., to be published in Eur. Phys. J. D (2014).
[5] Y. Fukaya, M. Maekawa, et al., Appl. Phys. Express 7, (2014) 056601.
[6] I. Mochizuki, et al., Phys. Rev. B 85 (2012) 245438.
[7] Y. Fukaya, et al., Phys. Rev. B 88 (2013) 205413.
[8] I. Mochizuki, et al., in preparation.
*
We thank the staff of the Photon Factory and the Accelerator Laboratory of KEK for their
support in the operation of the Slow Positron Facility. This work has been partly supported
by Grant-in-Aid for Scientific Research (S) 24221007 and for Young Scientists (B)
25800182 from the Japan Society for the Promotion of Science
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 18 11th International Workshop on Positron and Positronium Chemistry IT 11 Depth Profiles and Free Volume in Aircraft Primer Films*
J. D. Van Horn1,§, H. Chen1, Y. C. Jean1, W. Zhang2 and M. R. Jaworowski2
1
2
Department of Chemistry, University of Missouri-Kansas City, Kansas City, USA
Physical Sciences Department, United Technologies Research Center, East Hartford, USA
An understanding of materials properties is crucial for the design and use of materials
and coatings in extreme conditions. Positron annihilation lifetime spectroscopy (PALS) and
associated techniques provide non-destructive methods to study the free volume inside
polymeric materials, and to study material characteristics over a depth profile [1-3]. Cast free
films of solvent- and water-borne, non-chromated aerospace primers, when cured for about
one week, had very different water vapor transport (through-plane) behavior [4]. In addition,
both types of primer films showed strong anisotropic behavior in in-plane versus throughplane water vapor transport rates [4]. We evaluated the solvent- and water-borne aircraft
primer films and report the differences between the samples and their surface depth profiles.
In bulk PALS measurements, an aged,
solvent based film exhibited typical lifetimes
100000
and intensities for a particulate-containing
Front Face
Back Face
polymer film on both faces. In contrast,
aqueous-based films exhibited differences,
10000
s
dependent on the orientation of the face (see
t
n
u
Fig. 1). In all water-borne samples, the I3
o
C
value of the back of the sample was smaller
1000
and the associated free fractional volume
decreased in value. Primer film samples were
also evaluated with monoenergetic positron
100
185 225 265 305 345 385
beam techniques to generate depth profile
Channel Number
information. The heterogeneity in the samples
Fig.
1:
In
bulk
PALS
analysis,
a
significant
was verified by Doppler broadening of energy
spectroscopy (DBES). A model for the difference is observed in front and back
differences in the faces of the films, and their faces of an aqueous base aircraft primer
film.
layered structure is discussed.
Table 1. Mean pick-off lifetimes, intensities, free volumes and fractional free volumes for aqueousversus organic-base primer films in differing orientations. ((#) = calc. error in last sig. digit reported).
Primer Film Sample
Aqueous-base face-to-face
Aqueous-base back-to-back
Organic-base face-to-face
Organic-base back-to-back
 3 (ns)
2.00(1)
1.98(2)
2.20(2)
2.17(2)
I3 (%)
11.2(1)
6.8(1)
6.5(1)
7.2(1)
fv(Å3)
98(1)
96(2)
117(2)
114(2)
ffv(%)
1.98(4)
1.18(3)
1.39(3)
1.49(3)
[1] Y.C. Jean, et al., Progress in Organic Coatings 52 (2005) 1.
[2] D.W. Gidley, et al., Annual Review of Materials Research 36 (2006) 49.
[3] H. Chen, et al., Macromolecules 40 (2007) 7542.
[4] W. Zhang and M.R. Jaworowski, ECS Transactions 35 (2011) 53.
*
This work was performed under SERDP Project WP-1620.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 19 11th International Workshop on Positron and Positronium Chemistry IT 12 Depth Resolved Positron Beam Studies of Defect in Graphite
Varghese Anto Chirayath* and G. Amarendra§
Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102,
T.N, India
Graphite has been extensively studied owing to its interesting basic properties as well as
its applications in nuclear industry. Structural transformations induced by temperature and
pressure are of particular interest from applications point of view. Defects comprising of
point defects viz., vacancy and interstitial as well as their higher order complexes play a
crucial role in influencing these transformation. It was also recently found that the presence
of defects can induce magnetic ordering as well as alter its transport properties. Therefore,
the investigation of point defects, their clustering and thermal stability are of immense
interest in understanding physical and chemical properties of Graphite. Among various
experimental tools, positron annihilation spectroscopy has unique sensitivity and selectivity
to vacancy-defects and hence, can be effectively used to study graphite. We have carried out
detailed positron beam studies [1] on highly oriented pyrolytic graphite (HOPG) samples,
which are self ion irradiated two different doses. Depth-resolved S-parameter is monitored
on these samples subjected to various annealing temperatures, so as to get detailed
information on thermal stability of the defects. The similarities and differences in annealing
dynamics of the defect complexes between low and high dose samples will be presented
along with characteristic S-W correlation plots.
[1] Varghese Anto Chirayath, “Study of near surface defects using positrons and
Development of a pulsed positron beam system”, Ph.D thesis, Homi Bhabha National
Institute (HBNI), October 2013
* Present address: Sacred Heart College, Thevara-682013, Kerala, India
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 20 11th International Workshop on Positron and Positronium Chemistry IT 13 Application of Localized Annihilation of Positron and o-Ps
Y. Honda1,§, Y. Akiyama2 and S. Nishijima2
1
2
ISIR, Osaka University, Ibaraki, Osaka, Japan
Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Whenever some properties relating to functionality of material are evaluated by using
positron annihilation spectroscopy, special attention must be paid for the location where
positron and o-Ps annihilate. In many of such materials polarization due to functional group
or impurity would bring about inhomogeneous annihilation and formation of positronium and
annihilation of positron and positronium would be influenced by such local field. We have
investigated annihilation process of positron/o-Ps in PTFE related electrolyte membranes
through degradation process of the membrane, and found that o-Ps stays near the hydrophilic
site, i.e. just in the “skin” of inverse micelle which is formed by aggregation of hydrophilic
site. The lifetime of o-Ps is not so influenced by the condition of hydrophilic site where
HOMO level locates, but sensitive to the deformation of micellar skeleton. Localization of oPs would be caused by the presence of local electric field near the micelle. There is no such
local field in PTFE and annihilation would occur homogeneously. However it is known that
PTFE is composed of crystal part and amorphous part, which is found by measuring lifetime
of o-Ps. Such information would be used for reprocessing of PTFE and related materials.
Crown ether is known to form a chelate complex with radioactive cation which is
selected by the size of cavity. As o-Ps is trapped in the cavity of crown ether, the size of
cavity would be found by its lifetime. Positron can be used to find suitable extraction
condition of radioisotopes. HOMO level in crown ether also locates inside of the cavity.
Taking into account of the neutrality of o-Ps, it would be formed near the cavity and trapped
there. Much of the fallout from Fukushima nuclear power plant has been kept in clay around
there. The ability of storage of radioisotopes depends both on the electronic and the physical
structure. These properties can also be analyzed by positron as shown in another presentation.
Thus positron seems to approach a location of interest where chemical reaction is easy
to take place and eventually annihilate near there. However, it is crucial to identify where
positron and o-Ps annihilates and what kind of information can be brought.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 21 11th International Workshop on Positron and Positronium Chemistry IT 14 The Potential of Newer PET Radiopharmaceuticals in Enhancing the
Scientific Basis of Clinical Practice
Sandip Basu§
Radiation Medicine Centre, BARC, Tata Memorial Centre Annexe, Parel, Mumbai-400012,
India
Currently, 18F-fluorodeoxyglucose (18F-FDG) represents the most commonly utilized
PET tracer in the parlance of clinical imaging. The major two shortcoming of 18F-FDG for
using it for cancer is that [a] it is not an specific tracer for cancer and several benign
conditions especially the infection-inflammatory disorders demonstrate very high grade FDG
uptake; also [b] a number of malignancies like prostate cancer, hepatocellular carcinoma,
renal cell carcinoma, neuroendocrine tumors are not FDG avid and hence cannot be
adequately assessed by 18F-FDG-PET. Newer radiopharmaceuticals thus have been
investigated to (a) give more specific information and (b) provide better sensitivity. In
addition, they can aid in (c) complementing 18F-FDG-PET results by demonstrating valuable
information with respect to tumor biology (Table 1).
Table 1. The Salient Clinical expectations from Newer PET Radiopharmaceuticals
(a) Be more tumor-specific
(b) Provide superior sensitivity in FDG non-avid malignancies
(c) Complementing 18F-FDG-PET results in terms of tumor biology
The mostly investigated and promising newer radiopharmaceuticals include: [i]
Somatostatin receptor imaging tracers (e.g. 68Ga-DOTA-TOC/NOC/TATE), [ii] Amino acid
analogues(e.g. 11C-Methionine, 18F-fluoroethyl-L-tyrosine and L-3, 4-dihydroxy-6[18F]fluorophenylalanine), [iii] Hypoxia Imaging Tracers ([18F]Fluoromisonidazole,
64
[18F]EF5,
18F-FAZA,
Cu-ATSM
diacetyl-bis-N4-methylthiosemicarbazone),[iv]
Radiolabeled cell membrane components ([11C]Choline), [v] Tracers for lipid synthesis and
metabolism (11C-acetate), [vi] Radiolabeled nucleosides ([18F]Fluorothymidine). In the
present discourse will explore critically the potential clinical utilities of the newer PET
tracers in enhancing clinical oncology practice in the future. Their implications will be seen
particularly from the perspectives of: (a) accuracy of disease staging, (b) guiding therapy and
(c) assessing cancer biology and heterogeneity.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 22 IT 15 11th International Workshop on Positron and Positronium Chemistry Nanostructural Characterization of Complex Carbohydrate Polymers:
Recent Progress
M. Roussenova§ and M. A. Alam
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL,
United Kingdom
Carbohydrates have versatile physical and structural properties, linked to their
conformational degrees of freedom and propensity to form extended hydrogen bond networks
[1, 2]. These materials are of utmost importance for the pharmaceutical industry due to their
ability to form films, particles, and matrices with adjustable morphologies [2]. In addition,
under controlled conditions in the glassy state, they combine good physical stability with
excellent barrier properties towards gases [3] and organic molecules [4]. Carbohydrates are
thus commonly used in low water content dense matrices for the formulation of
pharmaceutical excipients and encapsulation matrices for labile bioactive ingredients [2].
It is now well recognised that in the glassy state, the molecular organisation of
carbohydrates has a profound effect on a number of their physical properties (e.g.: the
sorption of water [5] and the diffusion of small penetrant molecules [6]) which are of key
importance for the formulation of pharmaceutical encapsulants. In our recent studies, we used
Positron Annihilation Lifetime Spectroscopy (PALS) to probe the free volume in a variety of
carbohydrate polymers, and used the notion of molecular organisation to explain a number of
hitherto not well understood phenomena [7] observed in the physics of these systems. Here,
we present an overview of our recent and current PALS studies on model oligo- and polysaccharide systems [1, 7-11]. We show that PALS can be used to probe changes in
thermodynamic state, as well as the molecular organisation of these materials as a function of
temperature, matrix composition and water content [1, 7-11]. By combining our PALS data
with measurements from complementary techniques we aim to establish compositionstructure relationships for these model systems. This provides a promising route towards the
eventual rational design of pharmaceutical encapsulants, rather than the current largely trialand-error approach.
[1] M. Roussenova et al., Carbohydr. Polym. 102 (2014) 566.
[2] S. Kasapis et al., “Modern Biopolymer Science” (2009) San Diego: Academic Press.
[3] A. Schoonman et al., Biotechnol. Prog. 18 (2002) 139.
[4] Y. Gunning et al., Carbohydr. Res. 329 (2000), 377.
[5] J. Ubbink et al., Biomacromol. 8 (2007) 2862.
[6] S. Anandaraman et al., Food Technol. 40 (1986) 88.
[7] D. Kilburn et al., J. Phys. Chem. B 108 (2004) 12436.
[8] D. Kilburn et al., Nat. Mater. 5 (2006) 632.
[9] S. Townrow et al., J. Phys. Chem. B 111 (2007) 12643.
[10] S. Townrow et al., J. Phys. Chem. B 114 (2010) 1568.
[11] M. Roussenova et al., Biomacromol. 11 (2010) 3237.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 23 IT 16 11th International Workshop on Positron and Positronium Chemistry Ps Cooling in Silica-based Porous Materials
R. S. Brusa §
Department of Physics,University of Trento and INFN-TIFPA,38123 Povo (Tn), Italy
Positronium (Ps), the bound state of an electron and a positron, can be produced in
vacuum implanting positrons in a suitable material. The use of silica-based ordered or
disordered porous materials allows to obtain Ps at cryogenic temperature by decreasing the Ps
kinetic energy by collisional cooling [1-3]. Many open questions involving the process of Ps
cooling wait for an answer. New knowledge on Ps cooling and Ps spectroscopy open the
possibility to characterize closed porosities with size larger than five nanometers.
Furthermore, a huge number of cooled Ps in vacuum is necessary for new exciting
experiments like Ps spectroscopy and antimatter-matter comparison with antihydrogen beams
[4].
After a brief description of positronium formation mechanism in solids, the physics of
collisional Ps cooling will be discussed according to the latest results obtained by three
gammas spectroscopy, lifetime spectroscopy and time of flight spectroscopy measurements
carried out in ordered nanochannelled silicon [5-7].
Present running Ps spectroscopy [8] and antihydrogen experiments at CERN (AEgIS
experiment) [4] and TOF at NEPOMUC facility in Münich [5], will be presented. Future
possible use of Ps TOF and Ps spectroscopy for characterizing porosities will be discussed.
[1] S. Mariazzi, P. Bettotti, S. Larcheri, L. Toniutti and R. S. Brusa, Phys. Rev. B 81 (2010)
235418.
[2] S. Mariazzi,P. Bettotti, and R. S. Brusa, Phys. Rev. Lett. 104 (2010) 243401.
[3] “Positronium formation and cooling” R.S. Brusa and A. Dupasquier in International
School of Physics “Enrico Fermi” CLXXIV Course: “Physics with many positrons”,
edited by A. Dupasquier, A. P. Mills, Jr. and R.S. Brusa, (IOS, Amsterdam; SIF, Bologna
2010).
[4] M. Doser and the AEgIS collaboration, Physics Procedia 17 (2011) 49.
[5] L. Di Noto, S. Mariazzi, M. Bettonte, G. Nebbia, R. S. Brusa, Eur. Phys. J. D 66 (2012)
118.
[6] S Mariazzi, L Di Noto, L Ravelli, W Egger and R S Brusa, Journal of Physics:
Conference Series 443 (2013) 012061.
[7] R. S. Brusa, L. Di Noto, G. Nebbia, S. Mariazzi, Journal of Physics: Conference Series
505 (2014) 012038.
[8] L Penasa, L Di Noto, M Bettonte, S Mariazzi, G Nebbia and R S Brusa, Journal of
Physics: Conference Series 505 (2014) 012031.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 24 11th International Workshop on Positron and Positronium Chemistry IT 17 Positronium Annihilation in Mesoporous Silica Thin Films*
Chunqing He§, Bangyun Xiong, Wenfeng Mao, Xiuqin Tang
Key Laboratory of Nuclear Solid State Physics Hubei Province
School of Physics and Technology, Wuhan University, Wuhan 430072, China
Various silica thin films were deposited on Si wafers via a sol-gel method, using either
triblock copolymers or a cationic surfactant as structure-directing agents. Positronium (Ps)
formation and annihilation in the prepared mesoporous films with various structures were
studied using positron annihilation lifetime spectroscopy (PALS), Doppler Broadening of
annihilation radiation (DBAR) and Ps time-of-flight (Ps-TOF) measurements based on slow
positron beams. Issues about porosities, pore surfaces and pore morphologies on Ps
annihilation characteristics in mesopores will be presented.
1. Strong correlations between positronium 3γ annihilation fraction, S parameter and
porosity of the mesoporous silica films with isolated pores are obtained, which may
provide a complementary method to determine closed porosities of mesoporous silica
films by DBAR.
2. Ps emission/3γ annihilation depends not only on the pore interconnectivity but also on
pore morphologies due to Ps localization in larger pores;
3. Pore entrance size of cage-like pores may be estimated by PALS from Ps lifetime
trapped in connecting channels between cages of thin films with surface treatment, or
from the emission energy of cooled Ps from mesoporous thin films using Ps-TOF
measurements;
4. Because of the nature of Ps confinement in nano-channels, orientation of tubal pores
could be distinguished by measuring S, W parameters of positron annihilation in
ordered pores aligning along silica film surface using DBAR.
[1] B. Xiong, et al., J. Appl. Phys. 115/9 (2014) 094303.
[2] B. Xiong, et al., Phys. Lett. A. 378 (2014) 249.
[3] C. He, et al., Chem. Phys. Lett. 590 (2013) 97.
[4] C. He, et al., Phys. Rev. B 86 (2012) 075415.
[5] C. He, et al., Phys. Rev. B 75 (2007) 195404.
[6] C. He, et al., Appl. Phys. Lett. 91 (2007) 024102.
*This work was supported in part by National Natural Science Foundation of China (NSFC)
under Grants 10975108 & 11375132, and the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 25 IT 18 11th International Workshop on Positron and Positronium Chemistry Positron Annihilation Study in Metal-Organic Frameworks (MOFs)
Dhanadeep Dutta1,2,§, Jeremy I. Feldblyum3,4 David W. Gidley2, James Imirzian2, Ming
Liu5,6, Adam J. Matzger3,4, Richard S. Vallery7 and Antek G. Wong-Foy3
1
Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai-400 085, India
Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan
48109, USA
3
Department of Chemistry, University of Michigan, 930 North University Street, Ann Arbor,
Michigan 48109, USA
4
Macromolecular Science and Engineering, University of Michigan, 2300 Hayward Avenue,
Ann Arbor, Michigan 48109-2136, USA
5
NIST Polymers Division, 100 Bureau Dr. M/S 8541, Gaithersburg, Maryland 20899-8541,
USA
6
Nuclear Reactor Program, Department of Nuclear Engineering, North Carolina State
University, P.O. Box 7909, Raleigh, North Carolina 27695, USA
7
Department of Physics, Grand Valley State University, 151 Padnos Hall, Allendale,
Michigan 49401, USA
2
Metal-organic framework crystals have attracted immense interest over the last decade
because of their application in gas storage, separation and catalysis. Positronium has shown
great promise as a unique, in situ probe to reveal the pore structure in these new crystals.
Positronium is seen to exist in a delocalized state in these self-assembled metal-organic
framework crystals with large (~1.5 nm) cell sizes. The transport properties of long-lived
triplet positronium hypothesized to be in a Bloch-state was probed for the first time with
simple positron annihilation lifetime technique [1]. Delocalized positronium has shown
unprecedented high mobility driven primarily by weak phonon. The unique behaviour of long
lived positronium in metal organic frameworks will be discussed. The evolution of nano scale
pore structure during chemical exposure as well as the collapse of pores under humidity will
also be discussed.
[1] D. Dutta et al., Phys. Rev. Lett. 110 (2013) 197403.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 26 IT 19 11th International Workshop on Positron and Positronium Chemistry Evidence for a Positron Bound State on the Surface of a Topological
Insulator and Details of a New Positron Beam System for Materials Studies
Under Development at The University of Texas at Arlington*
A. H. Weiss1,§, K. Shastry1, B. Barbiellini2, B. A. Assaf2, D. Heiman2, P. V. Joglekar1,
Z. H. Lim1, and A. R. Koymen1
1
Physics Department, The University of Texas at Arlington, Arlington, TX 76019-0059 USA
2
Physics Department, Northeastern University, Boston, MA 02115 USA
Experiments carried out in our laboratory have demonstrated that Positron
Annihilation induced Auger spectroscopy (PAES) has greatly enhanced surface selectivity
relative to electron based surface spectroscopies such as Electron induced Auger
Spectroscopy or XPS. This sensitivity stems from the fact that positrons implanted into a
metal or semiconductor at low energies have a high probability of becoming trapped in an
surface localized state before they annihilate. Consequently the information carried by the
annihilation-induced signals (including Auger electrons and gamma rays) originates from the
top-most atomic layer.
First we will present the results of studies of a topological insulator (Bi2Te2Se) system
in which a magnetically guided positron beam was used to deposit positrons at the surface of
the material. The energy spectra and intensities of electrons and gamma rays emitted as a
result of the positron irradiation were measured. The electron energy spectra showed features
that can be identified with Positron Annihilation induced Auger transitions from Bi, Te, and
Se providing evidence that the incident positrons were trapped into a surface localized bound
state at the time of annihilation. Changes in the gamma ray spectra indicating an increased
emission of Ps as the sample temperature was raised are consistent with thermal desorption of
Ps from a positron or Ps bound state on the surface. These two measurements provide strong
evidence for a positron bound surface state suggests that positron annihilation can be used to
selectively probe the critically important top most layer of topological insulator system.
We will conclude the talk with a description of next generation high flux variable
energy position beam facility for materials studies (Fig. 1). This new system will employ a
high efficiency cryogenic moderator system and will incorporate both a time of flight
positron annihilation induced Auger electron spectrometer and a 2 detector Doppler
broadened annihilation gamma spectrometer systems for the study of both external and
internal surfaces.
Fig 1. Advanced Positron Beam System For Materials Studies [Under Development]
* We gratefully acknowledge support from the NSF under MRI 1338130 and DMR-
0907007.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 27 IT 20 11th International Workshop on Positron and Positronium Chemistry AIST Positron Probe Microanalyzer and its Application
N. Oshima§
Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial
Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
The AIST positron probe microanalyzer (PPMA) is a positron lifetime measurement
system using a pulsed and brightness enhanced slow positron beam [1]. A positron beam
produced by an electron linear accelerator [2] is brightness enhanced by focusing the beam
with a magnetic lens at a transmission type remoderator [3]. The surface of the remoderator, a
150 nm thick Ni foil, is cleaned by atomic hydrogen treatment in vacuum. The remoderated
positrons are again accelerated and focused on the sample by an objective lens. A specially
designed electro-static acceleration tube can adjust the beam energy over the wide range (1–
30 keV) while keeping the beam trajectory almost the same. The beam diameter is 30 -100
micrometers at the sample [4]. The beam is pulsed with a combination of two kinds of
bunchers to measure positron lifetimes. Positron lifetime can be measured with a time
resolution of 200-300 ps [5]. Typical counting rate of gamma-rays during a positron lifetime
measurement is ~103 s-1.
So far, we have performed defect/pore analysis of various samples by using advantage
of the AIST-PPMA i.e., positron annihilation lifetime spectroscopy (PALS) with good
special resolution and high count rates. Analytical methods with the PPMA (i.e. how the
PPMA was used) so far performed can be categorized as follows:
(i) defect/pore analysis of small samples [6-9]
(ii) defect/pore analysis for many local spots in large samples [10-12]
(iii) systematic defect/pore analysis of large number of samples [13]
(iv) in-situ (in-air) defect/pore analysis of thin films [14, 15]
We will report about our recent progress on slow positron beam manipulation techniques
and experimental results concerning the AIST-PPMA.
[1] N. Oshima et al., Appl. Phys. Lett. 94 (2009) 194104.
[2] B. E. O'Rourke et al., Rev. Sci. Instrum. 82 (2011) 063302.
[3] N. Oshima et al., J. Appl. Phys. 103 (2008) 094916.
[4] N. Oshima et al., Mater. Sci. Forum 607 (2009) 238.
[5] N. Oshima et al., Rad. Phys. Chem. 78 (2009) 1096.
[6] A. Uedono et al., Jpn. J. Appl. Phys. 48 (2009) 120222.
[7] A. Uedono et al., Appl. Phys. 114 (2013) 084506.
[8] A. Uedono et al., J. Appl. Phys. 114 (2013) 184504.
[9] H. Tsuchida et al., J. Phys.: Conf. Ser. 262 (2011) 012060.
[10] N. Oshima et al., J. Phys.: Conf. Ser. 262 (2011) 012044.
[11] T. Doshida et al., ISIJ Int. l52 (2012) 198.
[12] T. Oka et al., Appl. Phys. Lett. 101 (2012) 203108.
[13] N. Oshima et al., in preparation.
[14] N. Oshima et al., Appl. Phys. Express 4 (2011) 066701.
[15] W. Zhou et al., Appl. Phys. Lett. 101 (2012) 014102.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 28 11th International Workshop on Positron and Positronium Chemistry IT 21 Positron-Annihilation Lifetime Spectroscopy using Electron
Bremsstrahlung
A. Wagner1,§, W. Anwand1, M. Butterling1, T. E. Cowan1,2, F. Fiedler1, M. Kempe1,2, and
R. Krause-Rehberg3
1
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics,
POB 510119, 01314Dresden, Germany
2
Technische Universität Dresden, POB 510119, 01062Dresden, Germany
3
Martin-Luther-Universität Halle-Wittenberg, Institute of Physics, 06099 Halle, Germany
A new type of an intense source of positrons for materials research has been set up at
the superconducting electron linear accelerator ELBE at Helmholtz-Zentrum DresdenRossendorf [1]. The source employs hard X-rays from electron-bremsstrahlung production
generating energetic electron-positron pairs inside the sample under investigation. In
comparison to pioneering works at a normal conducting electron machine [2], the new
installation makes use of continuous-wave (CW) beams which are only available a
superconducting accelerator. CW-operation allows performing experiments with significantly
reduced pile-up artefacts in the detectors while distributing X-ray bunches evenly over time.
The high-resolution timing of the accelerator with bunch lengths below 10 ps FWHM allows
positron annihilation lifetime spectroscopy (PALS) measurements with high timing
resolutions.
The new source is especially suited for materials which cannot be exposed to external
sources of positrons (low-energy positron beams, radioactive sources), either because they
are not qualified for vacuum conditions (fluids, gases, organic samples) or because they are
imposing hazardous conditions (high pressure, high temperature, intrinsic radioactivity) to
the source. The contribution will present examples of PALS studies for a variety of such
cases which had been performed recently.
Employing segmented detectors for the detection of both annihilation photons allows
for the first time to perform a tomographic reconstruction of the annihilation sites including
the annihilation lifetime [3]. Examples of 4-dimensional analysis (three spatial, one temporal)
of extended inhomogeneous samples will be presented.
[1] M. Butterling, W. Anwand, T.E. Cowan, A. Hartmann, M. Jungmann, R. KrauseRehberg, A. Krille, A. Wagner, Nucl. Instrum. Meth.B 269:22 (2011) 2623-2629.
[2] F.A. Selim, D. P. Wells, J. F. Harmon, J. Williams, J. Appl. Phys. 97 (2005) 113539.
[3] A. Wagner, W. Anwand, M. Butterling, T.E. Cowan, F. Fiedler, M. Kempe, R. KrauseRehberg, Defect and Diffusion Forum 331 (2012) 41.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 29 11th International Workshop on Positron and Positronium Chemistry Invited Presentations Cidade de Goa, Goa, India November 9­14, 2014 30 11th International Workshop on Positron and Positronium Chemistry IP 1 Positron Annihilation Spectroscopy and TEM Study of Zirconium Base
Alloys used for Nuclear Reactor Applications
D. Srivastava§
Materials Science Division, Bhabha Atomic Research Centre, Mumbai -400005, India
Positron annihilation spectroscopy (PAS) is nowadays well recognised as a powerful
tool of microstructure investigations in the field of condensed matter. PAS is the most
effective technique to characterize the defects which may be a point, line or volume defect.
Transmission electron microscopy is the most common tool to investigate the characteristics
of the defects in the material. PAS is now complimenting TEM in very effective manner to
understand the nature of defects. PAS is being employed in the phase transformation studies
mainly for early stages of transformation. The creation of defects during deformation as well
as annealing of the defect during recovery and recrystallization of the metallic material is
being studied by PAS in many alloy system. Coincidence Doppler Broadening is now able to
tell the chemical nature of the defect as well.
Zirconium base alloys are extensively used as structural material in thermal nuclear
power reactors due to their superior corrosion and mechanical properties. PAS has been
effectively used as quality control tool for thermo-mechanical treatments during fabrication
of the zirconium alloy component as well as during service in the reactor. In this
presentation PAS study of deformation, recovery and recrystallyzation behavior in Zircaloys
will be included. Precipitation behavior in Zircaloy and Zr-2.5Nb alloy study by will be also
presented. Some examples of nanocrystallization behavior of amorphous soft magnetic
material studied by PAS will be also highlighted. The irradiation induced defects
characterized by PAS and complimentary techniques would be discussed in this presentation.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 31 11th International Workshop on Positron and Positronium Chemistry IP 2 Phase Behavior of Water Confined in Nanodomain
Priya Maheshwari1,§, D. Dutta1, S. Mukherjee1, S. K. Sharma1, K. Sudarshan1,
P. K. Madhu2, S. K. Deshpande3, N. Raje4 and P. K. Pujari1
1
Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai, India
Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, India.
3
UGC-DAE Consortium for Scientific Research, Bhabha Atomic Research Centre, Mumbai,
India.
4
Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, India
2
The properties of liquids confined in nanopores are different from their bulk phase
owing to the combined effect of finite size, surface forces, surface anisotropy and reduced
dimensionality. In such nanoscale, the intermolecular interactions between the liquid and the
pore surface as well as within the liquid molecules should explicitly be considered in order to
understand these properties. The nanoscale confinement of water has attracted considerable
attention due to its relevance to fundamental physics, biological and geological processes as
well as technological developments at nanoscale. Nanoconfined water can be supercooled
below its freezing temperature and exhibit anomalous properties, which is attributed to the
effect of surface interactions which modify the hydrogen-bonded network resulting in the
formation of new phases.
Our studies using positron annihilation lifetime and Doppler broadening spectroscopy
revealed the new phase transition temperature of confined water. The dynamics of water in
confinement is probed through relaxation times measured using nuclear magnetic resonance
and dielectric relaxation techniques. The dependence of phase behavior on the configuration
of water was also probed. The present talk will summarize our recent result on phase
behavior of water confined in slit-like and cylindrical pores of clay and MCM 41,
respectively. The result on the structure and dynamics of water confined in MCM 41
nanopores at different hydration levels will also be discussed.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 32 11th International Workshop on Positron and Positronium Chemistry IP 3 Positronium Bubble Oscillation in Room Temperature Ionic Liquids
T. Hirade1,2,§
1
Nuclear Science and Engineering Center, Japan Atomic Energy Agency,
Tokai, 319-1195 Japan
2
Graduate School of Science and Engineering, Ibaraki University,
4-12-1 Nakanarusawa, Hitachi, Ibaraki, 316-8511 Japan
The shortest lifetimes on the positron annihilation lifetime spectra for room temperature
ionic liquids (RTIL) were anomalously long [1]. The positron age dependence of Sparameters and W-parameters obtained by the age momentum correlation (AMOC)
measurements
for
the
RTIL,
N,N,N-trimethyl-N-propylammonium
bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), showed very strange tendency at younger
age region than 1ns [2]. Probably, the most suitable explanation for the change of S and W
for RTIL is slow Ps bubble formation [2].
Positronium (Ps) has negative work function in insulating materials and forms a bubble,
so-called “Ps bubble”, in liquids. It is needed to lose energy to be in a stable bubble state.
However it is considered that this relaxation process is too fast to detect by the positron
annihilation lifetime (PAL) or AMOC measurements with the time resolution of 150-200ps.
The AMOC study for RTIL [2] indicated that the Ps bubble formation is slow. Therefore the
oscillation of the bubble size is expected to be seen by PAL or AMOC measurements.
The ortho-Ps pick off annihilation probability depends on the size of the Ps bubble and
hence the oscillation on the PAL spectra is expected. In the case of usual liquids, bubble
formation time is, probably, very fast and then there have been no report of the oscillation
observed by PAL with the time resolution of about 150-200ps. Now the bubble formation in
RTIL is slow and it is expected to be able to see the oscillation on the PAL spectra.
If the ortho-Ps annihilation lifetime
of 3.35ns is applied, ortho-Ps annihilation
becomes more than para-Ps annihilation at
around the positron age of 300ps. The
para-Ps annihilation might be slower at the
young positron age region in RTIL, and
then the ortho-Ps annihilation can be more
than para-Ps annihilation at around 500ps
at latest. It means that the oscillation was
expected to be seen around the positron
Fig.1 Positron age dependence of the oscillation
age of 400-500ps.
component appeared on lifetime spectrum of
The result for TMPA-TFSI was
TMPA-TFSI at 25C.
indicated in Fig.1. This result strongly
indicated that the Ps bubble formation in RTIL must be slow. Moreover, PAL measurement
can be a strong tool to investigate the viscoelastic properties of RTIL to study the structure in
the sab-nano meter scale.
[1] T. Hirade, Materials Science Forum 607 (2009) 232.
[2] T. Hirade, T. Oka, Journal of Physics: Conference Series 443 (2013) 012060.
*This research was partially supported by a Ministry of Education, Culture, Sports, Science
and Technology Grant-in-Aid for Scientific Research (C), 23600011, 2011-2014.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 33 IP 4 11th International Workshop on Positron and Positronium Chemistry Characterization of Interfaces in Binary and Ternary Polymer Blends by
Positron Lifetime Spectroscopy
C. Ranganathaiah§
Department of Studies in Physics & Centre for Materials Science and Technology, University
of Mysore, Manasagangotri, Mysore-570006, India
In the last few decades blending of polymers had shown that many physical and
mechanical properties of polymers can be significantly improved. Polymer blending is
generally mixing of two or more structurally different polymers or copolymers resulting in a
range of properties, not deliverable by any of the constituents. Miscibility and phaseseparation phenomena of polymer blends hence received significant attention in polymer
applications [1]. To predict and enhance the blend properties, it is important to understand the
nature and the underlying mechanism of blending at the molecular level. One way is to
investigate the correlation between free-volume and miscibility level in blends [2]. Of the
several methods available for characterizing structure and properties of polymer blends, only
few methods are capable of characterizing free-volume properties due to the very small size
and its complex evolution. Positron lifetime Spectroscopy (PLS) has been mainly employed
in monitoring the ortho-positronium annihilation lifetimes in polymers to measure free
volume. A miscible blend is a single-phase system with compact packing of the polymeric
chains/segments due configuration/conformational changes upon blending. Differential
Scanning Calorimetry (DSC) is commonly used to test a blend if it is miscible or immiscible.
Of late free volume characterization is used for such studies [1] in polymers blends.
However, just free volume monitoring fails to provide the composition dependent
miscibility like the DSC method. To overcome this limitation, an alternative approach based
on hydrodynamic interactions has been developed to get the above information from the same
o-Ps lifetime measurements. This has led to the development of a new method [1,2] of
measuring composition dependent miscibility level in binary and ternary polymer blends
characterizing miscible and partially miscible blends and also interface characteristics in
immiscible blends. This turns out be a useful method to understand the characteristics of
interfaces which decide the miscibility level of the blend and their end applications. The
interactions between the blend components has a direct bearing on the strength of adhesion at
the interface and hence the hydrodynamic interaction. The development of this method will
be briefly introduced and its application to few binary [1,2] and ternary blends [3] will be
presented and discussed in the light of available literature data. The veracity of the method is
tested by suitably modifying the interfaces in these blends and evaluating the miscibility
results.
[1] A.M. Jamieson et.al in Polymer Physics: From Suspensions to Nanocomposites and
Beyond, L. A. Utracki and A. M. Jamieson (Ed.,) John Wiley, New York 2010, p.494.
[2] C. Ranganathaiah and G. N. Kumaraswamy, J. Appl. Polym. Sci 111 (2009) 577-588.
[3] Meghala and C. Ranganathaiah Polymer 53 (2012) 842-850.
§
e-mail: [email protected];[email protected]
Cidade de Goa, Goa, India November 9­14, 2014 34 11th International Workshop on Positron and Positronium Chemistry IP 5 Positron Annihilation Spectroscopic Studies of Multiferroic
Bi1-xPrxFeO3 Nanocrystalline Compounds
Jincemon Cyriac1, M. T. Rahul1, Nandakumar Kalarikkal1,2 and P. M. G. Nambissan3,§
1
School of Pure & Applied Physics, 2 International and Inter University Centre for
Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala 686560,
India
3
Applied Nuclear Physics Division, Saha Institute of Nuclear Physics, Kolkata 700064, India
The advent of multiferroic compounds like BiFeO3 and its modified forms has opened
up new avenues of research [1] and positron annihilation spectroscopy is very supportive for
the studies of their defect properties. Positron lifetime (PL) and coincidence Doppler
broadening spectroscopic (CDBS) experiments were carried out on BiFeO3 samples doped
with Pr (in place of Bi) in different concentrations (x = 0, 0.05, …, 0.3). The experiments
were carried out with the source-sample assembly in vacuum to avoid air, moisture and
absorbed gases.
1.6
5
10
4
10
3
10
2
10
1
10
0
x=0
x = 0.15
x = 0.3
0
50
Ratio of area-normalized counts
Coincidence counts
10
100 150 200 250 300 350 400
x=0
x = 0.15
x = 0.3
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0
5
10
15
20
-3
p L (10
Channel number (25 ps/channel)
25
30
35
40
m 0 c)
Fig. 2. The CDBS ratio curves. Fig. 1. Peak-normalized PL spectra The peak-normalized PL spectra of a few samples (x = 0, 0.15 and 0.3) are shown in
Fig. 1. The spectra yielded three components, the defect-related component 2 representing an
admixture of lifetimes of positrons annihilating within the vacancy-type defects in the
nanocrystallites and those getting annihilated at the nanocrystallite surfaces. When Pr3+ ions
are added, a number of Bi3+ vacancies are occupied and positron trapping is reduced. From x
= 0.15 to 0.3, I2 decreased marginally but 2 has increased from 311 to 338 ps, indicating
many of the vacancies are filled by Pr3+ ions and more number of positrons are diffusing to
the surfaces of the crystallites. The CDBS ratio curves showed that the doped samples have
features markedly different from those of the x = 0 sample (Fig. 2). The enhancement of the
peak at pL = 20×10-3 m0c due to positron annihilation with the 2p electrons of oxygen
suggests increased trapping in cationic vacancy defects. The change of lattice parameters
(3.9661-3.9248Å) or the crystallite sizes (28.6-34.2nm) due to doping were inconsequential
as they were below the thermal diffusion length of positrons.
[1] A. Mukherjee et al., J. Phys. D: Appl. Phys. 46 (2013) 495309.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 35 IP 6 11th International Workshop on Positron and Positronium Chemistry Positronium Chemistry in Liquids - First Investigations at the
GiPS Setup
M. Butterling1,2,§, D. Zvezhinskiy3,4, S. V. Stepanov3,4, A. Wagner1, W. Anwand1,
R. Krause-Rehberg2 and T. E. Cowan1
1
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, POB 510119,
01314Dresden, Germany
2
Martin-Luther-Universität Halle-Wittenberg, Institute ofPhysics, Von-Danckelmann-Platz 3,
06120 Halle(Saale), Germany
3
Institute of Theoretical and Experimental Physics, B. Cheremushkinskaya 25, 117218
Moscow, Russia
4
National Research Nuclear University “MEPhI”, Kashirskoyeshosse 31, 115409, Moscow,
Russia
The GiPS setup [1] at the radiation source ELBE (Electron Linac for beams with
high Brilliance and low Emittance) at Helmholtz-Zentrum Dresden-Rossendorf allows for the
investigation of positronium chemistry in liquids by using the Age-Momentum Correlation
(AMOC) technique. The advantages of this setup are the absence of typical contributions
from the positron source, a good timing resolution (< 180 ps FWHM) as well as a perfect
signal-to-noise ratio in positron annihilation lifetime spectroscopy (PALS). This allows
recording high-quality spectra and a simplified data analysis. Therefore, the setup is wellsuited for the application and verification of the blob model for liquids where positron
lifetime data is interpreted by means of radiolysis-induced reactions amongst the particles
and molecules in the medium instead of the common three-exponential approach [2].
For this reason, investigations of pure water at various temperatures and aqueous
solutions of KNO3 with different solute concentrations were performed at GiPS. A
comparison with known results successfully approved the ability of the setup for the
investigation of liquids. The radiolysis fit model could be successfully applied to the data
(PALS and AMOC) and explains differences in annihilation characteristics depending on
temperature and solute concentration by means of physical-chemical reactions. In addition to
that, the presence of quasi-free positronium [3] will be discussed using the AMOC data.
[1] M. Butterling, W. Anwand, T.E. Cowan, A. Hartmann, M. Jungmann, R. Krause
Rehberg, A. Krille, A. Wagner, Nucl. Instrum. Meth. B 269:22 (2011) 2623-2629.
[2] S.V. Stepanov, V.M. Byakov, D.S. Zvezhinskiy, G. Duplâtre, R.R. Nurmukhametov, P.S.
Stepanov, Advances in Physical Chemistry 2012 (2012) 431962.
[3] S.V. Stepanov, G. Duplâtre, V.M. Byakov, D.S. Zvezhinskiy, V.S. Subrahmanyam, Acta
Physica Polonica A 125(4) (2014) 770.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 36 IP 7 11th International Workshop on Positron and Positronium Chemistry A Dynamical Calculation Method of an Electron and a Positron Slowing
Down Process in Liquid Water
Takeshi Kai1,§, Akinari Yokoya1, Masatoshi Ukai2 and Ritsuko Watanabe1
1
Japan Atomic Energy Agency, 2-4 Shirakatashirane, Tokai, Naka, Ibaraki, 319-1195, Japan
2
Tokyo University of Agriculture and Technology, Koganei-shi, Tokyo 184-8588, Japan
Slowing down process of electrons ejected from water molecules in a liquid phase plays
a substantial role in the spatial distribution of those electrons and the distribution determines
following chemical processes in water radiolysis or biological damage induction by ionizing
radiation. The slowing down process has been studied by both theoretical and experimental
approaches so far. We have developed a dynamical calculation code of the electrons to
calculate precisely the process in liquid water [1]. The code consists essentially of a
Newtonian equation and a time-evolutional Monte-Carlo method. It, however, has been
employed cross sections in a gas phase.
Cross sections for rotational- and phononmodes excitation significantly contribute to the
electron slowing down process. We, however,
have no data of the cross sections of liquid
phase. Currently we calculated the cross
sections using an optical approximation [2] with
dielectric functions reported in a literature [3].
We improved our code [1] using the cross
sections of a liquid phase in this study.
Fig.
Thermalization
lengths
of
an
incident
We calculated thermalization lengths of an
electron. Solid line; present, ○; [3], □; [4]
electron injected into liquid water in energy
region from 0.1 eV to 100 keV. Figure shows thermalization lengths of an electron injected
into liquid water in energy region from 0.1 eV to 100 keV using our code improved in this
study. The figure also shows the experimental ones previously reported [4,5]. Our results are
in good agreement with the previous ones. We suggested that the code using our data of the
cross sections of a liquid phase is reasonable to simulate precisely slowing down process. In
web site [6], we show a movie for the slowing down process of the electron ejected from
water molecules in liquid water irradiated with a high-energy electron.
In the same manner as electron-molecular collisions, we can calculate the cross sections
of a liquid phase by positron-molecular collisions [2], and it is also possible to develop
positron-electron dynamical-calculation code from improvement of our code [1]. In this
conference, we propose a dynamical calculation method of an electron and a positron slowing
down process in liquid water, and our plan for a simulation method of positronium
production around a terminal of an incident positron decelerated in liquid water.
[1] T. Kai et al, Radiat. Phys. Chem. 102 (2014) 16.
[2] J. C. Ashley, Journal of Electron Spectroscopy and Related Phenomena 50 (1990) 323.
[3] H. Yada, M. Nagai, and K. Tanaka, Chem. Phys. Lett. 464 (2008) 166.
[4] ICRU, Stopping Powers for Electrons and Positrons, Report 37, (1984).
[5] V. V. Konovalov, A. M. Raitsimring, Yu. D. Tsvetkov, Radiat. Phys. Chem. 32 (1988)
623.
[6] http://nsedwww.tokai-sc.jaea.go.jp/ers/radiation/en/refa/index.html
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 37 11th International Workshop on Positron and Positronium Chemistry Oral Presentation Cidade de Goa, Goa, India November 9­14, 2014 38 OP 1 11th International Workshop on Positron and Positronium Chemistry Accounting for Lack of “Nano-effect” in a Thermoset/Clay
Nanocomposite: A Positron Annihilation Study
S.K. Rath1,§, K. Sudarshan2, M. Patri1 and P. K. Pujari2
1
2
Naval Materials Research Laboratory, Shil-Badlapur Road, Ambernath, India
Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
Composite materials dispersed with nanometer-sized reinforcing fillers are widely
reported to have the potential to improve the barrier and mechanical properties compared to
micro-composites or pristine polymers. Higher degree of reinforcements and barrier
properties at lower level of nanofiller loading (<5 wt%) is termed as the “Nano-Effect” [1].
However, in the present study we report the lack of so called “nano-effect” in case of
unsaturated polyester/clay nanocomposites. A series of cross-linked polyester/clay
nanocomposites were prepared by dispersing organically modified nanoclay at different
loadings. Transmission electron microscopy of the nanocomposites revealed intercalated
dispersion morphology of the clay layers in the crosslinked polymer matrix. The thermomechanical property measurements by
flexural and dynamic mechanical
analysis revealed progressive decrease
in flexural strength and storage modulus
with clay loading. Further, the alpha
relaxation
temperature
decreased
monotonically with clay loading. Water
sorption kinetics of the nanocomposites
revealed progressive increase in the
equilibrium water uptake but a
decreasing
trend
of
diffusivity
coefficient with clay loading.
Effect of clay loading on free
volume size and distribution of the
nanocomposites was investigated by
positron
annihilation
lifetime
Fig.1 Free volume radius distribution
spectroscopy. The studies revealed
increased fractional free volume with clay loading implying disruption of chain packing
efficiency for the nanocomposites. Another interesting feature is the existence of a higher
free volume element centered at 4.5 Å, which become more pronounced with clay loading as
seen from Fig. 1. Structure-property correlations have been developed based on these
findings to account for the lack of nano-effect in this most widely used thermoset polymer.
[1] D. R. Paul, L. M. Robson, Polymer 49 (2008) 3187.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 39 OP 2 11th International Workshop on Positron and Positronium Chemistry Carborane-Siloxane Polymers and Cross-Linked Hybrid Elastomers
Studied by Positron Annihilation Lifetime Spectroscopy and Differential
Scanning Calorimetry
D. Hughes1,§, M. V. Roussenova1, P. Beavis2, A. Swain2 and M. A. Alam1
1
H. H. Wills Physics Laboratory, School of Physics, University of Bristol, Bristol BS8 1TL,
United Kingdom
2
Atomic Weapons Establishment, Aldermaston, Reading, RG7 4PR, United Kingdom
The modification of poly(dimethylsiloxane) (PDMS, -[Si(CH3)2O]n-) by the chemical
inclusion of meta-carborane (m-CB, -C2B10H12-) into the polymer backbone has been shown
to produce materials with significantly enhanced thermal and chemical stability [1] compared
to neat PDMS. These materials, known commercially as DEXSILs (DEXSIL-x00: x
represents the number of siloxane units per monomer: -[Si(CH3)2-C2B10H12-Si(CH3)2{OSi(CH3)2}x-O]n-) can be used over a very wide temperature range and in extremely harsh
environments, including high levels of radiation [2], so are strong candidates for use in a
range of industrial applications. There have been few investigations into the nano-scale
properties of these materials (e.g. [2, 3]), which govern macroscopic properties, ultimately
determining their viability as materials for industrial applications.
In this study, a wide range of systems including the neat polymers outlined above and
hybrid cross-linked solid elastomers consisting of various blend ratios of a DEXSIL and
PDMS have been studied using positron annihilation lifetime spectroscopy (PALS) and
differential scanning calorimetry (DSC). This allows nano-structural characterization in terms
of the ‘local free-volume’ and thermodynamic characterization in the temperature range 100
– 350 K (from well below glass transition and well above melting temperatures).
It is observed that the transitions measured using DSC are apparent in the lifetime
parameters extracted from the lifetime spectra using PALS and are in good agreement with
the glass-transition (Tg) and the melting temperature (Tm) of the crystalline fraction that
exists within the systems studied. More importantly, we also observe that the incorporation of
m-CB into the polymer backbone acts to reduce the average size of the local free-volume
elements in the rubbery state, and increases the value of Tg, suggesting an enhanced interchain interaction upon inclusion of the m-CB. Also interesting is the fact that, in the hybrid
solid elastomeric systems, strong evidence of phase separation is seen both in DSC and PALS
data. The implications of these findings are discussed in terms of characterization of material
behavior as well their practical application potentials.
[1] E. N. Peters, Ind. End. Chem. Prod. Res. Dev. 23 (1984) 28.
[2] M. Patel et al., Poly. Deg. & Stab. 91 (2006) 548.
[3] J. Lewicki et al., Polymer 55(7) (2014) 1763.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 40 11th International Workshop on Positron and Positronium Chemistry OP 3 Gas Transport and Free Volume Study in Polyethylene Based Membranes
Pushkar N. Patil1,2,§ , R. Checchetto1, A. Miotello1, S. Aghion3, R. Ferragut3 and
R. S. Brusa1
1
2
Department of Physics, University of Trento, Povo, TN, Italy Institute for Polymers, Composites and Biomaterials, National Research Council, Napoli,
Italy
3
Department of Physics, Politecnico di Milano, Milano, Italy
Innovative gas selective polymeric membranes are essential in applications where gas
separation is required such as in the carbon dioxide capture and sequestration, in hydrogen
purification or in the dehydration of air as well as in advanced functional systems for gas
sensing. In this work we present an experimental study on the preparation and
characterization of nanocomposite membranes consisting of filler nanoparticles, namely
graphite nanoplatelets (GNPs) and magnetic Co nanoparticles, dispersed in a polymeric
matrix. The characterization of the size and concentration of free-volumes in these
nanocomposites is of fundamental importance to understand the gas transport mechanisms
and the gas separation properties of the membrane.
Polyethylene based polymeric membranes were selected as a matrix material because of
their good mechanical strength, ease processing and good compatibility with inorganic fillers.
Polymeric membranes with thickness in the 100 m range with different values of crosslinking densities have been prepared that give rise to different glass transition (Tg) values, as
confirmed by the Differential Scanning Calorimetry (DSC) measurements. Fourier transform
infra-red (FTIR) have been used to insure the complete crosslinking of the pure polymeric
membranes as well as the structural changes in the nanocomposite membranes. The gas
permeability, diffusion and selectivity for CO2, H2 and N2 were studied by gas permeation
measurements. A strong correlation between the crosslinking densities, glass transition
temperature and gas transport properties in the nanocomposite membranes was observed: the
permeability for all gases diminishes, in fact, by increasing the crosslinking density in the
polymers. Data analysis indicates that gas solubility only show minor variations whereas the
diffusion constant changes significantly as a function of crosslinking density.
The correlation between the free volumes, as studied by positron annihilation lifetime
spectroscopy (PALS), and gas transport through the nanocomposite membrane, as studied by
gas phase permeation technique, will also be discussed through the Cohen and Turnbull
equation:
  V  
 D  A exp
(1)  V 
f


where D is a Gas diffusion constant, A is a constant weakly dependent on temperature, γ is
an overlap parameter and V* is the minimal free volume size equal to the gas molecule while
Vf is the free volume fraction of the polymeric membranes.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 41 OP 4 11th International Workshop on Positron and Positronium Chemistry The Effect of UV Irradiation on per-fluorinated Sulfonic Acid/PTFE
Copolymer Studied by Positron Annihilation
Hamdy F. M. Mohamed§, E. E. Abdel-Hady, M. O. Abdel-Hamed and Aya H. Mohamed
Physics Department, Faculty of Science, Minia University, B.O. 61519 Minia, Egypt
Fumapem® F-1050 is a commercially available per-fluorinated sulfonic acid/PTFE
copolymer membrane used as the electrolyte in polymer electrolyte fuel cells. Proton
conductivity and thermal stability in the polymer membrane are highly important factors
which controls the overall performance of the fuel cells. The proton conductivity must be
affected by the electronic state near the ion exchange site, namely hydrophilic site, as well as
the structure of nanoscale spaces (free volume). The free volume holes in polymers play a
crucial role in determining its physical properties e.g., conductivity, permeability, thermal
stability, etc. Little is known about the role of free volume in a multiphase system like
Fumapem® F-1050. The Positron Annihilation Lifetime (PAL) technique has been
established as a powerful probe for microstructures of polymers, in particular, angstrom-sized
free volume holes. Therefore, we initiated a study on the free volume structure of Fumapem®
F-1050 membranes by using the PAL technique to correlate it with independently measured
proton conductivity for as received and UV irradiated samples. PAL spectra for all the
samples were measured at temperatures from 30oC up to 140oC (heating run) and then
cooling up to 25oC (cooling run). The temperature dependence of the ortho-positronium
lifetime (3) and its intensity (I3) exhibited little change between the cooling and heating runs,
so that the behavior appears to be irreversible. The variations of 3 with temperature for as
received sample showed transitions at 95oC (heating run) and at 81oC (cooling run). This
transition is corresponding to the glass transition temperature which is associated with the
onset of long-range mobility of both the main- and side-chains. The proton conductivity for
as received sample was measured as a function of UV irradiation time and temperature. A
correlation between the free volume and proton conductivity will be discussed for
unirradiated and UV irradiated samples.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 42 OP 5 11th International Workshop on Positron and Positronium Chemistry High-Precision Calculation of Loosely Bound States of LiPs+ and NaPs+
T. Yamashita§ and Y. Kino
Department of Chemistry, Tohoku University, Sendai 980-8578, Japan
Characteristics of atoms, molecules and ions are mainly attributed to their electronic
states. In particular, behavior of outermost shell electrons strongly contributes the chemical
reactions and binding mechanisms of molecules. A positron, an anti-matter of an electron,
can be bound to atoms or molecules and annihilates with one of the electrons in them
emitting some gamma rays. The positron exists near the outermost electrons due to a
repulsive Coulombic force between the positron and inner cation core of the atom. Since the
annihilation occurs depending on the electron density, the gamma rays reflect the details of
the wave functions of the outermost shell electrons.
Studies of positron-atom bound states can be a first step to search for a novel binding
mechanism of exotic atom/molecule and investigate the behavior of outermost shell
electrons. Positronic alkali atom is one of the best model systems for accurate investigations
because it can be regarded as a simple three-body system: a valence electron, a positron and
the residual cation core. A lot of theoretical calculations have been performed by using this
approximation and have revealed that a lithium and a sodium atom can form loosely bound
states (LiPs+ and NaPs+) with positron [1-2]. Since the binding energies are found to be three
orders of magnitude smaller than the lowest threshold energy, five or more significant figures
are required for the numerical calculation to confirm the existence of the bound states.
Recently, not only theoretical calculations but also some experimental studies to measure the
poitron-atom binding energy have been performed using laser-assisted photorecombination
[3]. Thus, a precise calculation of binding energies becomes more important.
However, the binding energy strongly depends on the model potential between the
cation core and valence electron. We calculated the model potential so as to reproduce higher
excitation levels of the atom as well as fine structure splittings. We also consider relativistic
corrections for this system.
High-precision calculation including relativistic effects is required for the loosely bound
states. For this purpose, we employ the Gaussian Expansion Method (GEM) [4] where the
three-body system is described with the positron-alkali atom configuration as well as the
positronium-alkali cation configuration. We pointed out that the fraction was small but
played an indispensable role [5]. The model potential between the alkali cation core and
valence electron is based on the potential proposed by Albright et al. [6] and is determined
numerically to reproduce up to highly excited levels and fine structure splittings. Relativistic
corrections are calculated within the first order perturbation theory including terms of a
momentum correction, Darwin, retardation, spin-spin and annihilation. Significance of the
total correction can be seen as contributions to binding energies, which are 0.22% for LiPs+
and 8.2% for NaPs+.
[1]
[2]
[3]
[4]
[5]
[6]
§
G. G. Ryzhikh and J.Mitroy, Phys. Rev. Lett. 79 (1997) 4124.
J. Yuan, B. D. Esry, T. Morishita and C. D. Lin, Phys. Rev. A 58 (1998) R4.
C. M. Surko et al, New J. Phys. 14 (2012) 065004.
E. Hiyama, Y. Kino and M. Kamimura, Prog. Part. Nucl. Phys. 51 (2003) 223.
Y. Kubota and Y. Kino, New J. Phys. 10 (2008) 023038.
B. J. Albright, K. Bartschat and P. R. Flick, J. Phys. B 26 (1993) 337.
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 43 11th International Workshop on Positron and Positronium Chemistry OP 6 Kinetic Energy of Ps formed by Ore Mechanism in Ar Gas
Y. Sano1,§, Y. Kino1, T. Oka1, 2 and T. Sekine2
1
2
Department of Chemistry, Tohoku University, Sendai, Japan
Institute for Excellence in Higher Education, Tohoku University, Sendai, Japan
Positron annihilation in dense gas has been studied to investigate a correlation between
positronium (Ps) and gas molecules. However, Ps annihilation with gas should depend
strongly on the kinetic energy of Ps, and Ps itself forms in the gas by the Ore mechanism. To
take Ps slowing down into account, the kinetic energy of Ps is crucial to investigate Ps
annihilation in gas.
The energy range of Ore gap of Ar gas is from 9 eV (Ps formation threshold) to 11.7 eV
(first electronic excitation threshold of Ar); the kinetic energy of Ps formed by Ore
mechanism is expected to be in the range from 0 eV to 2.7 eV. From a view point of atomic
physics, the Ps formation cross-section in a dilute Ar gas is in the range between 9 eV and100
eV. In dense Ar gas, Ps with a kinetic energy more than 6.8 eV would break up into a positron
and an electron by a collision [1]. In spite of the initial kinetic energy of Ps depends on Ar
gas density, unfortunately, it has not been measured precisely.
We performed a positron annihilation age-momentum correlation (AMOC)
measurement in Ar gas for 5.0 MPa and 7.5 MPa at room temperature, to observe the initial
kinetic energy of Ps and to reveal the Ps slowing down process below 6.8 eV. Time resolution
of this system was 300 ps at the full width at half maximum (FWHM). Energy resolution of
this system was 1.23 keV at 511 keV at FWHM. The positron source (22Na, 0.5 MBq) was
sandwiched between two sheets of 5 μm of the Ni foil (purity > 99%). The positron source
was placed in the center of a cylindrical high-pressure vessel with a diameter of 2.8 cm and a
height of 5.0 cm.
Doppler broadening of p-Ps annihilation gamma-ray is smaller than that of the free
positron annihilation gamma-ray. The p-Ps component was observed within 1 ns. By
separating the free positron component and p-Ps component, we determined the kinetic
energy of Ps (Eps) in every time step. Ps lost its energy down to 1 eV (2 eV) for the pressure
of 7.5 MPa (5.0 MPa) in this time region. The energy loss of Ps is written by
2 nM m
3
dEPs
  m Ar Ps2 2mPs EPs (t)(EPs (t)  kBT )
2
dt
 M Ar  mPs 
(1)
Where
is the Ps-Ar momentum transfer cross-section,
the Ar mass,
the positron
the Boltzmann constant, and is temperature [2]. As a
mass, a number density of gas,
first approximation, we assumed that
was constant in this energy range and we fitted Eq.
(1) to experimental values. The initial kinetic energy of Ps in Ar gas was 3.8eV and the
(1<Eps<3.8eV) was 0.017 nm-2. In the number density of 1.98 nm-3 (75 amagat) and 1.3
nm-3 (50 amagat), the kinetic energy of Ps was larger than the upper limit of 2.7 eV of Ore
gap.
[1] S. Armitage, D. E. Leslie, A. J. Garner and G. Laricchia, Phys. Rev. Lett. 89 (2002)
173402.
[2] Y. Nagashima, M. Kakimoto, T. Hyodo, A. Ichimura, T. Chang, J. Deng, T. Akahane, T.
Chiba, K. Suzuki, B. T. A. McKeeand A. T. Stewart, Phys. Rev. A 52 (1995) 258.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 44 OP 7 11th International Workshop on Positron and Positronium Chemistry Effect of Yttria Nanoparticles on Steels for Nuclear Applications*
I. Bartošová1,§, M. Dománková2 and V. Slugeň1
1
Institute of Nuclear and Physical Engineering, Slovak University of Technology, Bratislava,
Slovakia
2
Department of Materials Science, Slovak University of Technology, Trnava, Slovakia
Oxide dispersion strengthened steels (ODS) are candidate materials for the first wall of
the actual proposed nuclear fusion reactors. They contain Y2O3 nanoparticles which restrict
dislocation movement in the microstructure. The experiments reported in this work focus on
the investigation of EP450 ODS by Positron annihilation lifetime spectroscopy (PALS) and
Transmission electron microscopy (TEM) in as received state and after helium implantation.
Helium implantation simulates radiation damage without inconvenient radiation associated
with neutron irradiation. Additionally, the selected area electron diffraction (SAD) together
with TEM revealed expected Y2O3 particles and chromium-rich carbides M23C6 in the base
material. Positron measurements indicate a high concentration of small defects distributed in
the sample. Due to high yttrium affinity it seems that positrons are attracted and captured by
defects in the vicinity of yttria oxides. TEM was used for identification of microstructural
changes after helium implantation, since yttria oxide particles can act as low energy sites
capable of trapping helium.
*
Financial support from Slovak scientific agencies VEGA 1/0204/2013 and APVV AK48 are
highly acknowledged.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 45 11th International Workshop on Positron and Positronium Chemistry OP 8 Positron Annihilation Spectroscopy of Dilute Uranium Based Alloys
S. Mukherjee1, S. K. Sharma1, V. Sinha2, M. T. Saify3, S. K. Jha3 and P. K. Pujari1,§
1
Radiochemistry Division, 2Metallic Fuels Division, 3Atomic Fuel Division,
Bhabha Atomic Research Center, Mumbai, India, 400085
Dilute U-Zr and U-Mo alloys have been characterized for the first time using positron
annihilation spectroscopy. In case of U-Zr alloys with Zr wt. = 2 - 10 %, the chemical
signature in the matter-antimatter annihilation gamma and the positron lifetime data suggests
that majority of positrons are annihilating from Zr sites in the as-cast alloys. The results
indicate presence of Zr rich nano-agglomerates in the as-cast alloys which have a higher
positron affinity as compared to the U matrix. A minimum agglomerate size of ~2 nm
diameter has been calculated from the difference in positron affinity between the
agglomerates and the matrix. Upon annealing, the Zr signature in the annihilation gamma
photons vanishes suggesting that the Zr agglomerates diffuse out of U matrix and form
micron-sized precipitates. The second part corresponds to the positron annihilation studies of
U-Mo alloy (Mo wt. % = 8-10 %). While the phase diagram suggests that room temperature
U-Mo alloys should consist of α-U and MoU2 phases but it has been recently shown that with
increased Mo concentration ( wt.% > 8), the γ phase is stabilized at room temperature. This
phase is desirable because of its better stability under irradiating condition as compared to αU. We have presented here the results of defect study of as-cast U-Mo alloys prepared by a
novel metallurgy process developed by one of the authors. The alloys were subsequently hot
rolled and the evolution of the defect characteristics is discussed. The subsequent thermal
treatment necessary to anneal out the defects while preserving the metastable γ phase is
sought to be achieved using positron annihilation spectroscopy.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 46 OP 9 11th International Workshop on Positron and Positronium Chemistry The investigation of Implanted Alloys using Positron Annihilation
Spectroscopy with Combination of Nanoindentation Technique
V. Sabelová1,§, V. Kršjak2, M. Petriska1 and V. Slugeň1
1
Faculty of Electrical Engineering and Information Technology, Slovak University of
Technology in Bratislava, Ilkovičova 3, 81219 Bratislava, Slovakia
2
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Positron annihilation methods based on slow positron beam are very effective tools for
characterization of surface layers in the meaning of small open volume defects. In this work,
Doppler broadening spectroscopy was used for investigation of Fe-Cr model alloys implanted
with hydrogen and helium ions. The implantations were performed by linear accelerator at
temperatures below 100°C. S-parameter depth profiles of the implanted samples up to 1.5µm
were compared to the results of nanoindentation technique. Isochronal annealing up to 700°C
with the step of 100°C was applied on the helium and hydrogen implanted samples in order
to investigate embrittlement of material. Both experimental techniques show a good
correlation and together they provide an interesting insight to radiation hardening.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 47 OP 10 11th International Workshop on Positron and Positronium Chemistry Effect of Alkali Metal Ions in Vacancy Defect and Defect Cluster in MgO
Nanocrystallites by Positron Annihilation Spectroscopy
S. Selvakumar1,§, J. Sivasankari2, K. Sivaji3, T. Semba1, A. Uedono1 and S. Sankar2
1
Division of Applied Physics, University of Tsukuba, Ibaraki 305-8573, Japan
Department of Physics, MIT Campus, Anna University, Chennai -600044, India
3
Department of Nuclear Physics, Guindy Campus, University of Madras, Chennai-600025,
India
2
Magnesium oxide (MgO) nanopowders had wide application in waste water treatment,
an additive to paints, catalysis and superconducting materials [1]. Nano magnesium oxide is
being used in a number of applications across multiple domains. The addition of alkali metals
with MgO, generated a significant increase of the catalytic activity [2, 3]. Hence, the present
study is aimed to synthesize alkali metal doped MgO nanostructures by solution combustion
method and to investigate the effect of dopants by XRD, SEM, TEM and positron
annihilation spectroscopy.
In the present work, a relatively simple auto-combustion method was used in the
synthesis of pure and 1% group I elements (Li, Na and K) doped MgO nanocrystallites.
XRD analysis reveals that all the MgO doped nanocrystals had cubic crystal structure. The
progressive incorporation of Li, Na and K ions into the MgO lattice was monitored by XRD.
SEM reveals the spherical structure for MgO: Na and with small porous spherical structure
for MgO: K. Positron annihilation lifetime and
Doppler broadening spectroscopy measurements
were performed for pure and doped MgO. Positron
lifetime data analysis gave four components for
pure and doped MgO. The lifetime τ1 is due to the
annihilation of positrons at grain and grain
boundaries. A defect-specific lifetime τ2 originates
from the annihilation of positrons at vacancy-type
defects within the grains. The longer lifetime
components τ3 and τ4 being the lifetime of
positrons trapped in the defects at the grain surfaces
and of ortho-positronium formed in the
intercrystalline regions. The variation of positron Fig. 1: Variation of S and W of asprepared and annealed MgO and Li,
lifetime values of Li, Na and K doped MgO
Na and K doped samples
confirms the interaction between the ions during the
annealing process. From coincidence Doppler broadening measurements, the positron
trapping sites were identified as vacancy clusters. Figure 1 represents the variation of S and
W of as prepared and annealed samples. At higher temperature, the S parameter decreases due
to particle growth and reduction in the defect concentration. It has been observed that
annealing at 800 °C, Li ion migrate to the vacancy site. The variation of lifetime components
and S parameter of doped and annealed samples will be presented.
[1] O. Medenbach et al., J. Opt. A: Pure Appl. Opt. 3 (2001) 174.
[2] L. Xu and G. Henkelman, Phys. Rev. B 77 (2008) 205404.
[3] J. Beheshtian, et al., Bull. Korean Chem. Soc. 33(6) (2012) 1925.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 48 11th International Workshop on Positron and Positronium Chemistry OP 11 Study of Positron Systematics in Li-irradiated Alumina (α-Al2O3)
P. V. Gaikwad1, S. K. Sharma2, S. Mukherjee2, Priya Maheshwari2, K. Sudarshan2, A.
Kshirsagar1 and P. K. Pujari2,§
1
2
Department of Physics, University of Pune, Pune, India 411007
Radiochemistry Division, Bhabha Atomic Research Center, Mumbai, India 400085
Lithium ion implantation and
subsequent annealing induced nanocluster
growth inside α-alumina matrix has been
studied using slow positron beam. The
sample was prepared by implanting 50
keV Li-ions with fluence of 5x1016
ions/cm2 on the alumina substrate. The ion
implanted sample was annealed at different
temperatures from 400 oC to 1100 oC. The
mean implantation depth of Li ion in
alumina was calculated using SRIM
simulations.
Doppler
broadening
annihilation radiation measurements have
been carried out in the annealed sample. Fig 1. Evolution of S-parameter vs positron beam
Positrons are preferentially trapped at Li energy plot for Li implanted alumina with
cluster due to their higher positron affinity different annealing temperatures
as compared to the alumina substrate. The
average lineshape parameter of the annihilation radiation (S-parameter) at the Li implantation
site increases with annealing temperature and is maximum at ~800 oC. Upon further
annealing, the S-parameter reduces which suggest either breaking up of the Li clusters or a
phase change in nanocluster. The latter scenario will make the matrix-cluster interface
incoherent causing preferential positron trapping at the cluster-matrix boundary. A similar
experiment with Li ion fluence of 1x1016 ions/cm2 showed no change in S-parameter with
increasing annealing temperatures suggesting a threshold dose for the formation of Li
nanoclusters in the matrix. The experimental data have been supported by DFT based
calculation.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 49 11th International Workshop on Positron and Positronium Chemistry OP 12 Unmanageable Defects in Proton-Irradiated Silicon: A Factual Outlook for
Positron Probing
N. Yu. Arutyunov1,4,§ , V. V. Emtsev2, M. Elsayed1, R. Krause-Rehberg1,
G. A. Oganesyan2, C. Kessler1, and V. V. Kozlovski3
1
Department of Physics, Martin Luther University, 06120 Halle, Germany
2
Ioffe Physico-Technical Institute, St. Petersburg 194021, Russia
3
St. Petersburg State Polytechnical University, St. Petersburg 195251, Russia
4
Institute of Electronics, Tashkent 700170, Uzbekistan
Though defects in silicon to be irradiated with electrons and protons of MeV energies
are accumulated similarly, with much higher rates in the case of protons, the production and
separation of Frenkel pairs occur quite differently, - chaotically and in cascades for the
electron and proton irradiation, respectively. For a variety of basic reasons, a fate of a
cascade is difficult to predict and a behavior of defects both under formation and annealing
proved to be a confused problem. This work is centered on the consequences of a relaxation
of cascades and defects formation within small limits of low doses (4 – 8·1013 cm–2) of MeV
proton irradiation of moderately doped n–FZ–Si[P≈7·1015cm–3] material. Low-temperature
positron annihilation lifetime and Hall effect measurements have been carried out at each
temperature of thorough isochronal annealing over the range of ~ 100 – 700 ºC [1, 2].
A distinctive feature of the positron annihilation data under consideration is that the
localization of positrons at the point defects of a vacancy type in the proton-irradiated silicon
occurs on the background of a comparatively less effective production of the acceptor-like
centers, whereas the latter, namely, the phosphorus-vacancy pairs dominate in the same
material irradiated with ~1 MeV electrons. According to the results of electrical
measurements, these thermally stable (up to Tannealing ≥ 600 – 700 ºC) positron traps are the
deep donors having the levels Ed > Ec – 0.24 eV; these defects include the atoms of
phosphorus. Disappearance of divacancies in the course of isochronal heating precedes the
commencement of annealing of the deep donors at Tannealing ≥ 320 ºC; the positron long-lived
lifetime values suggest involving, at least, two vacancies in their microstructure. These
defects are neutral (or, perhaps, electrically inactive) in the investigated material of n-type.
Annihilation radiation is emitted from the shallow and deeper positron states which are
affected by interaction with phonons. Being a few 10–12 – 10−13 cm2 (66 – 300 K) and
obeying ~T−3 law, the values of effective capture cross-section suggest phonon-assisted
cascade trapping of positrons by divacancies and by the phosphorus-vacancy complexes
having properties of the deep donors. The configuration and charge states of these positron
traps and divacancies as well as the activation energies of quasi-chemical reactions of defects
are considered in the light of the data obtained for the phonon-assisted cascade trapping of
positrons in the course of the isochronal annealing. A salient dissimilarity of the positron
trapping by defects in the proton-irradiated germanium of n-type is discussed in order to
illustrate further strategy for studying a role of the distribution of Frenkel pairs in forming the
radiation defects in silicon under the proton irradiation.
[1] N. Arutyunov et al., J. of Phys.: Condens. Matter 25 (2013) 035801.
[2] N. Arutyunov et al., AIP Conf. Proc. 1583 (2014) 41; Solid State Phenom. 205 (2014)
317.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 50 OP 13 11th International Workshop on Positron and Positronium Chemistry Wave Packet Dynamics of Vibrational Feshbach Resonances in Positron
Scattering from Fluoromethane *
L. Poveda1 and J. R. Mohallem2,§
1
2
Departamento de Física e Matemática, CEFET-MG, Belo Horizonte, MG, Brazil
Departmento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
The interaction of a low energy positron with the C  F stretching mode of the
Fluoromethane molecule is studied using time-dependent wave-packet dynamics [1]. A twodimensional potential energy surface describing the collinear coupling between the scattering
and vibrational coordinates was calibrated from a set of ab initio energies, computed within
the FNMC (finite nuclear mass correction) methodology [2]. The cross section for the = 0
 =1 inelastic channel depicts an onset behavior at the excitation threshold with a sharp
resonant peak, attributed to the positron capture by the target in a vibrational Feshbach
resonance [3].
The present approach allows for a precise dynamical description of this phenomenon,
which plays a leading role in resonant positron annihilation [3].
Fig. 1: 0  1 vibrational excitation cross section
as a function of the translational energy
[1] G. G. Balint-Kurti, R. N. Dixon, C. C. Marston, and A. J. Mulholland, Comput. Phys.
Commun. 63 (1991) 126.
[2] D. Assafrão and J. R. Mohallem, J. Phys. B: At. Mol. Opt. Phys. 43 (2010) 155204L;
Poveda, A. Dutra, J. R. Mohallem and D. Assafrão, Phys. Rev. A 87 (2013) 052702.
[3] G. F. Gribakin, J. A. Young, and C. M. Surko, Rev. Mod. Phys. 82 (2010) 2557.
*
§
Supported by CNPq and Fapemig.
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 51 11th International Workshop on Positron and Positronium Chemistry OP 14 H  Production from Collisions Between Positronium
and keV Antiprotons for GBAR
P. Comini2 and P. –A. Hervieux1,§
1
Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS and Université de
Strasbourg, BP 43, F-67034 Strasbourg Cedex, France
2
DSM/IRFU/SPP, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex, France
The GBAR experiment (Gravitational Behaviour of Antihydrogen at Rest) [1] was
recently accepted at CERN at its Antiproton Decelerator facility. The aim of the experiment
is to perform the free fall of antihydrogen atoms ( H ) to test the weak equivalence principle
for antimatter. In order to reduce the uncertainty on the initial H velocity, ultra-cold
antihydrogen atoms of a few neV are required. The key idea of the GBAR experiment is to
use H  ions that can be cooled with techniques established for ultra-cold atoms. The H  ions
will be produced from collisions between keV antiprotons ( p ) and a positronium (Ps) cloud
through two successive reactions: (1) p  Ps ( n p , l p )  H ( n h , l h )  e

(3-body
H ( n h , l h )  Ps ( n p , l p )  H   e  (4-body reaction). A
theoretical study of reactions (1) & (2) has been undertaken in order to optimize the
H  production by choosing accurately the energy of the p beam and the Ps excited state (np,
lp). An exhaustive set of cross sections has been obtained for both reactions, from Ps(1s) to
Ps(3d) and considering H states up to nh=4. Contrary to reaction (2), reaction (1) has been
already widely studied, mainly through the reverse reaction of Ps formation (see for instance
[2]), but for the sake of theoretical consistency, it has been decided to apply the same
theoretical model, namely the Continuum Distorted Wave – Final State model (CDW-FS), to
compute the cross sections of both reactions at the same level of approximation [4].
Concerning reaction (2), the highly correlated system formed by H  has been treated
carefully, using three different wave functions proposed for H  . In the case of reaction (1),
the results show an enhancement of the H production toward low p kinetic energies, when
nh and np increase. This agrees with experimental data [3] and previous calculations [2]. For
reaction (2), a nearly resonant behavior close to threshold is observed for excited
positronium, when H is in its ground state. For both reactions, above 1 keV p energy, the
highest cross sections are obtained with Ps (2p). In order to estimate the H  production in the
reaction chamber of the GBAR experiment and optimize other experimental parameters such
as laser power for Ps excitation and delays between pulses, a simulation based on the present
cross sections, solving Bloch equations to compute the Ps populations, has been
implemented. This highlights the challenges to be solved in this critical part of GBAR.
reaction)
[1]
[2]
[3]
[4]
§
and
(2)
The GBAR Collaboration 2011 CERN-SPSC-2011-029, SPSC-342.
J. Mitroy, Phys. Rev. A 52 (1995) 2859.
J. P. Merrison et al., Phys. Rev. Lett. 78 (1997) 2728.
P. Comini and P. –A. Hervieux, New Journal of Physics 15 (2013) 095022.
NJP Highlights of 2013' collection
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 52 11th International Workshop on Positron and Positronium Chemistry OP 15 Precise Measurement of Energy Spectrum of Orthopositronium Decay
S. Adachi1,§, T. Yamaji1, A. Ishida1, T. Namba2, S. Asai1 and T. Kobayashi2
1
Graduate School of Science, the University of Tokyo, Tokyo, Japan
International Center for Elementary Particle Physics, the University of Tokyo, Tokyo,
Japan
tree-level &  ()
800
700
phase space
600
500
400
300
200
100
0
0
0.1 0.2
0.3
0.4 0.5 0.6
energy(MeV)
Fig. 1: Theoretical spectra. Solid
black line: the phase space
calculation. Solid gray curve: the
tree-level
QED
calculation.
Dashed
black
curve:
the
calculation. 5
4
3
1
2
0
1
2
3
4
[1] Y. Kataoka, S. Asai, T. Kobayashi, Phys. Lett.
B 671 (2009) 219.
103
5
0.4 0.42 0.44 0.46 0.48 0.5 0.52 0.54
energy (MeV)
Positronium (Ps) is an ideal system for the
precision test of quantum electrodynamics (QED)
in bound state. Orthopositronium (o-Ps) decays
into three gamma rays dominantly, and their
energy spectrum has detail information on boundstate QED. Since the energy spectrum has the
differential information on the total decay rate, its
shape can be more sensitive for new physics than
the decay rate [1]. The purpose of this study is to
check the spectrum at the level accuracy
(0.4% at around 0.511MeV, Fig. 1).
We constructed a setup for the precise
measurement. Ps is created at silica aerogel in a
vacuum chamber, and its decay gamma rays are
measured with a LaBr3(Ce) scintillator. In this
setup, the materials around the Ps assembly and
the detector are well-controlled, and all their
responses are coded in a GEANT4 simulator in
detail.
After the measurement for about 3 months,
the obtained spectrum is compared with the
expected spectrum from the calculation and
the GEANT4 simulator. The difference between
them is shown in Fig. 2, and no significant
differences are observed. This measurement is a
first confirmation of the spectrum.
counts (a.u.)
2
Fig. 2: Difference between the
observed spectrum and the expected
spectrum from the calculation
and the GEANT4 simulation. The
solid line shows the line fitting
result.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 53 OP 16 11th International Workshop on Positron and Positronium Chemistry Positron Annihilation in Benzene, Aniline and Cyclohexane
K. Fedus§, A. Karbowski, D. Stolarz and G. P. Karwasz
Institute of Physics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
Positron annihilation in liquid cyclic hydrocarbons received relatively little
experimental attention [1,2]. Cyclohexane, benzene and aniline, in spite of their chemical and
structural similarities, seemed to show quite different positron lifetimes: τ1=142 ps for
benzene, τ1=214 ps cyclohexane and τ1=204 ps for aniline [2]. The second and third
components of lifetimes were reported rather similar τ2=440-480 ps and τ3=2.4-3.2 ns with
the intensity I3 of some 33-43%, see [2, 3] for detailed data. Gray et al. in the early work [1]
searched for the correlation of τ3 with the molecular polarizability. However, the interaction
between thermal positron and molecules is governed by scattering cross sections and the
polarizability is only one of the factors influencing the low-energy cross section.
Our measurements of positron scattering in the gas phase performed with the very lowenergy apparatus [3] showed that total cross sections in aniline and benzene practically
coincide in the 0.5-10 eV energy range while that of cyclohexane is by some 20-30% lower.
However, in order to deduce annihilation rates, some extrapolation of cross sections down to
thermal energies is needed. We did it recently [4] using modified effective-range theory but
the analysis requires some additional input on the scattering length; we used values obtained
by Surko and collaborators in their experiments on the annihilation in the gas phase [5].
Cross sections derived in this way in the zero-energy limit [4] contradict our gas phase
experiment [3]. This triggered present measurements of annihilation in the liquid phase.
Present measurements were performed with ORTEC PLS system, with RCA 8850
photomultipliers and St. Gobbain BC418 plastic scintillators, assuring a 180-190 ps time
resolution. 22Na source encapsulated in 7 μm kapton foil was used. The source immersed in
liquid was protected by 25 μm polyethylene foil. Measurements were performed at 295 K.
The LT programme by J. Kansy [6] was used to analyse spectra.
Differently to previous measurements [2] we report similar all three components in the
lifetime spectra for benzene and aniline (τ1=174±5 ps and τ1=181±7 ps, respectively with
I1=22%; τ2=474±8 ps and τ2=445±13 ps with I2=42%; and τ3=2.14 ns and τ2=2.25 ns for
benzene and aniline respectively). The first and second component in cyclohexane are longer:
τ1=225±6 ps and τ2=562±14 ps; the third component is similar to aniline, τ3=2.40 ns, but
shows a lower intensity, I3=30% vs I3=35%, respectively.
In the gas phase [3] we observed an enhanced cross section at 2-4 eV, i.e slightly above
the positronium-formation threshold; this effect was absent in cyclohexane. We speculate on
the correlation between the cross section for positronium formation in the gas phase and the
τ3 intensity. Further measurements on other benzene derivates are under way.
[1] P. R. Gray, C. F. Cook, G. P. Sturm Jr, J. Chem. Phys. 48 (1967) 1145.
[2] O. E. Mogensen, Positron Annihilation in Chemistry, Springer-Verlag, Berlin 1995.
[3] G. P. Karwasz et al., Acta Phys. Polonica 107 (2005) 666.
[4] K. Fedus and G. P. Karwasz, Acta Phys. Polonica 125 (2014) 829.
[5] G. F. Gribakin, J. A. Young, C. M. Surko, Rev. Mod. Phys. 82 (2010) 2557.
[6] J. Kansy, Mater. Sci. Forum 652 (2001) 363.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 54 11th International Workshop on Positron and Positronium Chemistry OP 17 Manifestation of the Tunnelling Effect in Positronium and Muonium
Liquid-phase Reactions
P. S. Stepanov1,2, V. M. Byakov1,2,3,§, S. V. Stepanov1,2 and A. G. Zaluzhnyi2
1
Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25,
117218, Moscow, Russia
2
National Research Nuclear University “MEPhI”, Kashirskoye shosse 31,
115409, Moscow, Russia
3
D. Mendeleyev University of Chemical Technology of Russia, Miusskaya sq., 9,
125047, Moscow, Russia
It is demonstrated that the rate constants k of the diffusion-controlled reactions of Psand Mu-atoms with a solute S, Ps + S => Product and Mu + S => Product, may be expressed
as a sum of two terms:
k = kd + kt = 4πDR + πνλ3/4 .
The first term, kd , is proportional to the coefficient D of mutual diffusion and to the reaction
radius R of the reagents. The second term, kt , is D-independent and characterizes the
efficiency of tunneling (electron or positron, or entirely Ps or Mu atom) to the scavenger S.
Coefficients ν and λ are defined by the well known Gamov factor for the tunneling
probability, ν·exp[-(r-R)/λ], where ν is the oscillation frequency of the tunneling particle and
λ is the penetration length of its wave function. The contribution of tunneling is revealed in
that the observable reaction rate constant k, extrapolated to the zero value of D, tends not to
zero but to a non-zero value. We have demonstrated that a number of the rate constants of the
Ps and Mu reactions in liquids with different diffusion coefficients of the reagents are
quantitatively described by the above equation.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 55 11th International Workshop on Positron and Positronium Chemistry OP 18 PLT and DBAR Investigations on MPDMAPP Doped PVA-PVP Blend
§
R. F. Bhajantri1, , V. Ravindrachary2, Blaise Lobo3, Sunil G. Rathod2 and H. Chandrappa1
1
Department of Physics, Karnatak University, Pavate Nagar, Dharwad - 580 003, India
2
Department of Physics, Mangalore University, Mangalagangotri - 574 199, India
3
Department of Physics, Karnatak Science College, Karnatak University, Dharwad 580001,
India
Positron is a nano-probe of free volume holes in polymeric materials [1]. It is sensitive
to chemical species like negative ions, radicals and polar groups in polymers, resulting in
inhibition and (or) quenching of positronium (Ps) [2,3]. Poly(vinylpyrrolidone) (PVP) is a
vinyl polymer possessing planar and highly polar side groups. Poly(vinyl alcohol) (PVA) is
semi-crystalline polymer possessing hydroxyl (OH) groups. When these two polymers are
mixed (equal proportion by weight), they form a miscible blend. The preparation of
MPDMAPP (1-(4-methylphenyl)-3-(4-N,N, dimethyl amino phenyl)-2-propen-1-one) doped
PVA-PVP blend is described elsewhere [4]. MPDMAPP was doped in PVA-PVP blend, in
the concentration range varying from 0.025 wt% up to 1 wt%. In this paper, the results of
Positron Lifetime (PLT) and Doppler Broadening of Annihilation Radiation (DBAR)
techniques on these films are described. Free volume size, trapping rate of positron and Ps in
the ordered (νo) and disordered regions (νd), respectively, of the polymeric blend were
calculated. The S-parameter of DBAR was found to be linearly related to the orthoPositronium (o-Ps) intensity I3. The o-Ps lifetime τ3 is found to change little, from 1.67 ns at
0.025 wt% dopant concentration to 1.69 ns at 0.5 wt% dopant level, but drops to 1.42 ns at 1
wt% dopant concentration, indicating the onset of phase separation. However, the o-Ps
intensity I3, S-parameter, and the trapping rates νo and νd show interesting variation in the
entire range of dopant concentration. The S-parameter shows an increase at low dopant
concentration from 0.025 wt% up to 0.1 wt%, beyond which it drops significantly. This is
supported by the XRD patterns of MPDMAPP doped PVA-PVP films, which reveals
dominant amorphous nature at low dopant concentration, and a semi-crystalline nature at
moderate and high concentration of the dopant.
Acknowledgement: The authors are thankful to DAE-BRNS, Govt. of India for a research
project (2010/37C/7/BRNS/832) and DST, Govt. of India for the research project
SR/FTP/PS-011/2010.
[1] Chia-Ming Huang, Eckard W. Hellmuth, Y. C. Jean, J. Phys. Chem. B 102 (1998) 2474.
[2] Blaise Lobo, M R Ranganath, T S G Ravi Chandran, G Venugopal Rao, V Ravindrachary
and S Gopal, Phys. Rev. B 59 (1999)13693.
[3] R Zhang, J Robles, J Kang, H Samha, H M Chen, Y C Jean Macromolecules 45
(2012) 2434.
[4] R.F. Bhajantri, V Ravindrachary, Boja Poojary, Ismayil, A Harisha and Vincent Crasta,
Polym. Eng. Sci. 49 (2009) 903.
§
e-mail: [email protected], [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 56 OP 19 11th International Workshop on Positron and Positronium Chemistry Physical Selectivity of Molecularly Imprinted Polymers Evaluated through
Free Volume Size Distributions Derived from Positron Lifetime
Spectroscopy
T. Pasang1 and C. Ranganathaiah1,2,§
1
Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore, India
2
Centre for Materials Science and Technology, Vijnana Bhavan, University of Mysore,
Manasagangotri, Mysore-570006, India
The technique of imprinting molecules of various sizes in a stable structure of polymer
matrix has derived multitudes of applications[1].Once the template molecule is extracted
from the polymer matrix, it leaves behind a cavity, which is both physically (size and shape)
and chemically (functional binding site) compatible to the particular template molecule.
Research in MIPs has emerged as an
attractive field owing to their wide
variety of applications like chemical and
biosensors, solid-phase extraction (SPE),
drug delivery systems etc. Plenty of
literature exists about the synthesis and
applications
of
MIPs
[2,3].
Unfortunately, Positron Annihilation
Lifetime Spectroscopy (PALS) a well
known technique to measure cavity sizes
precisely in the nanoscale is not being
used in the field of MIPs. So this method
capable of measuring nanopores is more
suitable to understand the physical
Fig. 1: Free volume radius distribution
selectivity of the MIPs better. With this
of different stages of MIP creation and
idea in mind, we have prepared
rebinding of the 2PP template molecule
molecular imprinted polymers (MIPs)
with methacrylic acid (MAA) as monomer and EGDMA as cross linker in different molar
ratio for three different size template molecules, viz. 4-Chlorophenol (4CP) (2.29 Ǻ), 2Nepthol (2NP) (3.36 Ǻ) and Phenolphthalein (PP) (4.47Ǻ). FTIR and the dye chemical
reactions are used to confirm the complete extraction of the template molecules from the
polymer matrix. The free volume size and its distribution have been derived from the
measured o-Ps lifetime spectra. Based on the free volume distribution analysis, the
percentage of functional cavities for the three template molecules are determined. Percentage
of functional binding cavities for 4-CP molecules is found out to be 70.2% and the rest are
native cavities [4]. Similarly for 2NP it is found to be 81.5% and for PP it is 100%.The PP
template molecule which is larger in size compared native cavity size, produces 100%
physical selectivity while 4CP template produces only 70% physical selectivity. Therefore,
PLS method proves to be very precise and accurate to determine the physical selectivity of
MIPs which are designed for specific sensor applications.
[1]
[2]
[3]
[4]
§
T. Pasang, C. Ranganathaiah, Polym. Eng. Sci. 54 (2014) 667.
C. Alexander, et al., J. Mol. Recognit. 19 (2006) 106.
N. Holland, et al., Polymer 51 (2010) 1578.
T. Pasang, C. Ranganathaiah, Ind. Eng. Chem. Res. 52 (2013) 7445.
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 57 OP 20 11th International Workshop on Positron and Positronium Chemistry Investigation of PCM Microcapsules at Low Temperature and High
Pressure by PALS Method*
B. Zgardzińska§, M. Tydda and A. Błażewicz
Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland
The positron annihilation lifetime spectroscopy was used to investigate the properties of
phase change material (PCM): the Micronal® DS 5001 X microcapsules from BASF The
Chemical Company. The microcapsules are composed of simple organic materials: the
polymer capsule shell and the paraffin core. As expected, at low temperature -150ºC, two
groups of free volumes were observed: the longest-lived can be ascribed to the polymer, the
other, of more complex structure – to the mixed alkanes. Both o-Ps components showed the
known effect of the intensity rise with positron irradiation time, however, the scale of that
rise was greatly reduced compared to neat materials. In the case of the core it can be the
result of mixed structure (our earlier study [1] has shown the decrease of intensity rise with
broadening the composition of paraffins), manifesting itself also in the shape of the MELT
spectrum. There was no destructive effect of temperature – repeated measurements after
cooling were fully reproducible.
With increasing the temperature up to -3ºC we have observed the short lifetime as for
alkane rigid phase, then the rotator-like phase in the range -3ºC - +26ºC and liquid phase
above +26ºC. This form of temperature dependence of PAL spectra is discussed.
Two high pressure experiments (up to 450 MPa) were performed: without gas access to
the sample enclosed in a vessel with pistons, and in argon atmosphere. In the first case there
was little effect limited to outer part of capsule aggregates; in the other one the gas
penetration destroyed the aggregates and the capsule shells.
The PALS results were compared with those performed by other methods: scanning
electron microscopy, laser diffraction study of particle size distribution.
[1] B. Zgardzińska, T. Goworek, Chem Phys. Lett. 547 (2012) 35.
* This
study is supported by the grant 2013/09/D/ST2/03712 of National Science Center in
Poland
§ e-mail:
[email protected]
Cidade de Goa, Goa, India November 9­14, 2014 58 11th International Workshop on Positron and Positronium Chemistry OP 21 Direct Correlation between Free Volume and Dielectric Constant in a
Fluorine-containing Polyimde Blend
R. Ramani1, R. Ramachandran2, G. Amarendra2 and S. Alam1,§
1
2
Polymer Science Division, DMSRDE, G.T. Road, Kanpur - 208 013
Materials Physics Division, Materials Science Group, IGCAR, Kalpakkam - 603 102
Polymer blending offers an attractive and simpler method in the development of new
polymeric materials compared to chemical synthesis and the blends often exhibit more
desirable characteristics than individual polymers [1]. The blending allows optimization of
some of the properties of the homopolymers and provide an economic way to create new
materials with desired properties. Thus, blending of polymers has been an important
industrial approach towards the development of novel polymeric materials. When a polymer
blend is formed, free volume is one of the properties that gets affected and the free volume is
closely related to dielectric constant () [2].
Herein, we report a motivating finding on the origin of dielectric constant in a
polyimide blend prepared using a fluorine-containing polymer and a polyimide probed in
terms of its available free volume, which is distinct from the generally observed behaviour in
fluorinated polyimides. For this study, a blend of poly (vinylidine fluoride-co-hexafluoro
propylene) and poly(ether imide) was chosen and the interaction between the two polymers
was studied using Fourier Transform Infrared Spectroscopy, X-ray diffraction,
Thermogravimetric analysis and Scanning Electron Microscopy. The blend was investigated
by Positron Annihilation Lifetime Spectroscopy (PALS), Doppler broadening (DB) and
Dielectric Analysis (DEA). The positron results reveal that with the increase in the fluorine
content in the blend, the ortho-positronium (o-Ps) intensity also increases which is different
from the commonly observed o-Ps inhibition
process in halogenated polymers.
The dielectric constant of a polyimde is
mainly influenced by its molecular polarizablity
and the free volume. The dielectric constant
decreases with the increase in free volume, due
to decrease in the number of polarizable
groups/unit volume. In the present case, with the
increase in the relative free volume content in
the blend, surprisingly, the dielectric constant
also increases (see Fig. 1). The reason for this
positive change has been identified. Other
experimental methods used such as capillary
rheometry, calorimetric measurements and
Fig. 1: Variation of dielectric constant
dynamic
mechanical
thermal
analysis
with relative free volume fraction.
supplement the results.
[1] L. A. Utracki, Polymer Alloys and Blends, Hanser Publishers, New York, 1989.
[2] G. Houghman, G. Tesero, A. Viehbeck and J.D. Chapple-Sokol, Macromolecules 27
(1994) 5964.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 59 OP 22 11th International Workshop on Positron and Positronium Chemistry PALS and DBAR Study on LiClO4 doped PVA - NaAlg Blend Based
Polymer Electrolyte
T. Sheela1, P.M.G. Nambissan3, V. Ravindrachary1, Blaise Lobo4, Vidyashree Hebbar1,
Jagadish Naik1 and R. F. Bhajantri2,§
1
Department of Physics, Karnatak University, Pavate Nagar, Dharwad - 580 003, India
2
Department of Physics, Mangalore University, Mangalagangotri - 574 199, India
3
Applied Nuclear Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhan Nagar,
Kolkata-700 064, India
4
Department of Physics, Karnatak Science College, Karnatak University, Dharwad 580001,
India
Solid polymer blend electrolytes (SPE) are promising materials, with potential
applications in advanced electrochemical technology. Positron Annihilation Spectroscopy
(PAS) has been successfully used to study the micro-structure of such materials [1]. The
electrolyte films of poly(vinyl alcohol) (PVA): sodium alginate (NaAlg) blend (composition
60:40 wt%) doped with different concentrations (up to 15 wt%) of lithium perchlorate
(LiClO4) salt were prepared by solution casting. A correlation between structural properties
and Ps formation probability with charge carrier concentration and ionic conductivity is
investigated. The spectroscopic results show that the Li+ ions interact with polymer chains
through hydrogen bonding. Mechanical properties of the composite films show an
enhancement in elastic nature. Differential Scanning Calorimetry (DSC) results show a single
glass transition temperature (Tg), thereby confirming the compatibility between PVA and
NaAlg to form a miscible blend. The X-Ray Diffraction (XRD) patterns show an increase in
degree of crystallinity. The highest ionic conductivity value of 3.81×10–5 S/cm is observed
for 5 wt% doping level, which indicates the addition of salt (LiClO4) increases the number of
mobile charge carriers (Li+ and ClO4-) and the degree of dissociation of LiClO4. The behavior
of S parameter obtained from Doppler Broadening Spectroscopy (DBAR), was interpreted in
terms of increased positron annihilation with low momentum electrons, and increase in
positronium (Ps) formation probability [2]. The positron lifetime (PALS) data shows that
both the inhibition of Ps formation and quenching of ortho-positronium (o-Ps), revealed by
the drop in both the o-Ps lifetime component (τ3) and the corresponding intensity (I3) [3].
Acknowledgement: The authors are thankful to DAE-BRNS, Govt. of India for the research
project (2010/37C/7/BRNS/832) and DST, Govt. of India for the research project
(SR/FTP/PS-011/2010).
[1] D. Bamford, G Dlubek, A Reiche, M A Alam, W Meyer, P Galvosas and F Rittig, J.
Chem. Phys. 115 (2001) 7260-7270.
[2] K Ito, Y Kobayashi, and A Nanasawa, Appl. Phys. Lett. 82 (2003) 654-656.
[3] R. F. Bhajantri, V Ravindrachary, A Harisha, C Ranganathaiah, G N Kumaraswamy.
Appl. Phys. A 87 (2007)797-805.
§
e-mail: [email protected], [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 60 11th International Workshop on Positron and Positronium Chemistry OP 23 Temperature Dependent Positron Annihilation Characterization of Fe
Based and Other Superconductors
D. Sanyal§
Variable Energy Cyclotron Centre, 1/AF, Bidhannagar, Kolkata 700064, India
Temperature dependent positron annihilation spectroscopy has been employed since
last 20 years to study the superconductivity induced changes in the positron annihilation
parameters in different superconductors. Recently superconductivity induced change in the
coincidence Doppler broadening of positron annihilation radiation line-shape parameter has
been observed in Fe based superconductors. The superconducting sample shows, on cooling
below ~40 K and towards Tc, a sharp decrease of S, the line-shape parameter, which gives
the fraction of suitably defined low momentum electrons as probed by the positrons. No such
decrease of S for the non-superconducting sample indicates the effect to be induced by
superconductivity. Detailed results along with the temperature dependent ratio-curve analysis
of the present samples and the earlier results will be presented.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 61 OP 24 11th International Workshop on Positron and Positronium Chemistry Investigation on the Oxygenation Effect of Porous Silicon from the EMD
by Positron Annihilation*
K. Sivaji1,§, R. Rajaraman2, C.S. Sundar2 and S. Selvakumar3
1
Materials Science Centre, Department of Nuclear Physics, University of Madras,
Guindy Campus, Chennai 600 025, INDIA.
2
Materials Science Division, IGCAR, Kalpakkam 603 102, INDIA.
3
Division of Applied Physics, University of Tsukuba, Ibaraki 305-8573, Japan
Porous Silicon (PS) has attracted a lot of attention owing to the nanostructures of
network of small Si particles, retaining its lattice structure and the efficient
photoluminescence in the visible region at room temperature [1]. The surface properties of
PS can be expected to play an important role due to their small microstructures and the high
density of surface states classified as dangling bonds and to its large internal surface area.
The electronic properties of PS in general depend upon a host of formation conditions.
Positron annihilation techniques throw light on the electronic structure, microstructural
defects, surface properties, free volumes etc. During preparation of porous silicon by
anodization the dangling bonds on the pore surface gets saturated by hydrogen, forming Si:H
complexes leading to open volume defects as in hydrogenated amorphous Si [2]. Effect of
heat treatment on PS has been studied with positron lifetime and Doppler broadening
measurement [3,4].
2D-ACAR is sensitive enough to reveal
the corresponding modification of surface
properties if the positrons were annihilating at
the pore surface. Our previous report of 2DACAR studies suggest that the annihilation
occurs at the pore surface [5]. In order to
confirm these results, studies on PS samples
annealed in oxygen environment are carried out
and the EMD is presented in Fig.1. The studies
momentum (p ) in mrad
suggests that, the hydrogen effusion occurred
Fig. 1 2D-ACAR cross sectional
due to the formation of Si:O complexes when
distributions
for PS - oxygenated at
heated in oxygen environment. A study of
100oC, 350oC and 650oC with that
positron trapped in the open volume defects, on
for un-oxygenated and bulk CSi.
the formation oxide layers from the pore
surface, yields useful information on the microstructural properties of PS.
The paper will present the details of these studies and bring out the EMD features
extracted by 2D-ACAR, as an important technique to understand the oxygenation effect and
defects in porous silicon.
x 104
18
Bulk CSi
16
15PS50 at 100oC - O
15PS50
2
15PS50 at 350oC - O
2
14
15PS50 at 650oC - O
Counts (arb.units)
2
12
10
8
6
4
2
0
0
2
4
6
8
10
12
x
[1] L.T. Canham, Appl. Phys. Lett. 57, (1990) 1046; V. Lehmann and U. Gosele, Appl. Phys.
Lett. 58 (1991) 856.
[2] Y.J. He, M. Hasegawa, R. Lee, S. Berko, David Adler and Ai-Lien Jung, Phys. Rev. B 33
(1986) 5924.
[3] R. Suzuki, Phys. Rev. B 49 (1994) 17484.
[4] S. Dannefear, C. Wiebe, and D. Kerr, J. Appl. Phys. 84 (1998) 6559.
[5] K. Sivaji, C. S. Sunder, G. Amarendra, R. Rajaraman, S. Sankar, Physica Status Solidi
(c) Current Topics in Solid State Physics 4 (10) (2007) 3654.
§
e-mail: [email protected], [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 62 OP 25 11th International Workshop on Positron and Positronium Chemistry Positron Annihilation Spectroscopy of Eu and Dy Doped α’-Sr2SiO4:
Understanding Difference in their Local Site Occupancy
S. K. Gupta§, K. Sudarshan, S. K. Sharma, P. K. Pujari and V. Natarajan
Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
Studies of dopant ion distribution in hosts with multiple coordination/sites have
attracted much attention, because they lead to better understanding of the correlations
between structure and properties such as color, magnetic behavior, catalytic activity, and
optical properties etc., which are strongly dependent on the occupation of these two sites by
metal ions. In the structure of Sr2SiO4, there are two different Sr sites: one having
coordination number 9 (Sr(2)) and the other with coordination number 10 (Sr(1)). Sr (1)
polyhedron has more symmetric environment having hexagonal pseudo-symmetry than Sr(2).
We have doped 0.5 mol % Eu and Dy in α’-Sr2SiO4. Time resolved fluorescence
spectroscopy(TRFS) studies showed that that Eu(III) ions occupy both Sr(1) and Sr(2) sites,
whereas Dy(III) ions occupy only Sr(2) sites [1, 2]. In order to probe the electronic
environment of positron trapping centers in the doped strontium silicate, coincidence Doppler
broadening (CDB) studies were carried out on pure Sr2SiO4 and Eu and Dy doped sample.
While profiles of both undoped and doped samples are similar, there is as considerable
increase in area under high momentum region for Dy doped sample. This indicates the
difference in the chemical surrounding of annihilation sites in the Dy doped sample. To get
further insight into nature of defects, positron annihilation lifetimes were measured. The
increase in 1 is higher than expected due to oxygen vacancies suggesting that vacancy, in this
case is - cation vacancies (V"Sr) [3]. Average lifetime for Dy doped samples is higher than Eu
doped samples. This may be because of different site occupancy of Dy compared to Eu as
evident from other studies.
[1] S.K. Gupta, M. Mohapatra, S. Kaity, V. Natarajan and S.V.Godbole, Journal of
Luminescence, 132 (2012) 1329.
[2] E. R. Vance, J. V. Hanna and J. H. Hadley, Adv. Appl. Ceram. 111 (2012) 94.
[3] S.K. Gupta, M. Kumar, V. Natarajan and S.V. Godbole, Optical Material, 35 (2013)
2320.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 63 OP 26 11th International Workshop on Positron and Positronium Chemistry Vacancy Structure in Niobium Monoxide Ceramics by Means
of PALS, DBS Spectroscopy and QM Calculations*
A. A. Valeeva1,2,§, M. Butterling3 , M. G. Kostenko1 and A. A. Rempel1,2
1
Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences,
Pervomaiskaya 91, Ekaterinburg 620990, Russia
2
Ural Federal University named after the First President of Russia B.N. Yeltsin
620002, Ekaterinburg, Mira 19, Russia
3
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics,
POB 510119, 01314 Dresden, Germany
This contribution presents a study of the structural vacancies in ordered niobium
monoxide NbO by means of positron annihilation lifetime spectroscopy (PALS), Doppler
broadening spectroscopy (DBS) and first-principal quantum mechanical (QM) calculations.
This ceramic oxide contains an abnormally large number of vacancies (up to 25 at.%) on both
metal and non-metal sublattices and nevertheless is stoichiometric NbO1.00 without any
homogeneity range [1]. So the aim of present work was to study an electron density of the
structural vacancies in order to understand the stability of ordered phase of NbO. An answer
on this question is important in energy saving applications of oxide ceramics.
The measurements of PALS and DBS spectra of NbO were performed at the GiPS setup
[2] at the radiation source ELBE (Electron Linac for beams with high Brilliance and
low Emittance) at Helmhotz-Zentrum Dresden-Rossendorf. The advantages of this setup are
the absence of typically contributions from the positron source, a good timing resolution (<
180 ps FWHM) as well as a perfect signal-to-noise ratio in positron lifetime spectra. This
allows for recording high-quality spectra and simplifies the data analysis.
QM calculations were performed with the PWSCF code of the QUANTUMESPRESSO package [3] based on plane waves (PW) and pseudo-potentials. Niobium 4s4p
semi-core levels were included in the Nb pseudopotential.
In NbO, two components in PLT spectra were observed. According to calculations, the
short component (171 ps with 83 % of intensity) can be ascribed to delocalized positron
states in fully ordered compound. Second component of 336 ps should be ascribed to
localized trapping state in niobium vacancies. According to QM calculations, such long
lifetime is due to very low volume density of electrons in charged niobium vacancy in
compare to four times higher density in oxygen vacancy. This result is supported by DBS
which shows both oxygen and niobium environment of positron annihilation sites.
[1] A. Valeeva, H. Schroettner, and A. A. Rempel, Inorganic Materials 50 (2014) 398.
[2] M. Butterling, W. Anwand, Thomas E. Cowan, A. Hartmann, M. Jungmann, R. KrauseRehberg, A. Krille, A. Wagner, Nucl. Instrum. Meth. B 269:22 (2011) 2623.
[3] P. Giannozzi et al., J. Phys. Condens. Matter 21 (2009) 395502.
*
We thank the group from the ELBE centre for the measurements. This work was partially
financially supported by the Ural Branch of the Russian Academy of Sciences under project
12-P-234-2003 and RFBR No. 14-02-00636.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 64 OP 27 11th International Workshop on Positron and Positronium Chemistry Effect of Local Electric Field on the Positronium Formation in Irradiated
Polymer.
V. Ravindrachary1,§, Ismyail2, R. F. Bhajantri3, Rohan S. Sagar1, Guruswamy1
and P. K. Pujari4
1
2
Department of Physics, Mangalore University, Mangalagangotri, 574 199 (India)
Department of Physics, Manipal Institute of Technology, Manipal University, Manipal,
3
Department of Physics, Karnatak University, Dharwad 574 199 (India)
4
Radiochemistry Division, BARC, Trombay, Mumbai-400 085 (India)
When positrons are injected into polymers, can form positronium (Ps), (bound state of
an electron and a positron): para-positronium (p-Ps) (positron and electron have opposite
spins) and ortho-positronium (o-Ps) (spins are parallel). The great interest in the study of
polymers using positron lies in the fact that the Ps formation probability, intensity I, and
lifetime τ, depend on the physical and chemical properties of the solids. Generally, the o-Ps
intensity I3 is believed to be related to the free-volume density and is known to depend on
several parameters like chemical composition, mechanical history of the sample, free radicals
due to radiation, built up electric field due to charge carrier etc. The irradiation of polymers
with ionizing radiations alters the physico-chemical properties of the polymer and the studies
on these irradiated polymers are of rapidly increasing area of research interest [1].
Pure Poly (methyl methacrylate) (PMMA) polymer films (thickness 80–100 µm) were
prepared by solution casting method and were subjected to 8 MeV electron beam irradiation
up to 300 kGy doses. The Positron Annihilation Lifetime spectra for irradiated PMMA were
recorded using conventional fast-fast coincidence spectrometer (resolution 240ps) with BaF2
detectors. The obtained data were analyzed into three lifetime components using a computer
program PATFIT-88 & the third component τ3, I3 is attributed to o-Ps lifetime component and
is associated with the pick-off annihilation of o-Ps.
The observed positron results are understood by invoking the built up electric field due
to free radical formation during irradiation. The observed variations of o-Ps intensity I3
suggests that the irradiation of PMMA will creates free radicals (Ḣ) within the polymer and
these created free radicals (Ḣ) as well as positrons are expected to be trapped by the polar
methyl carboxylate (COOCH3) group of the polymer upto 100kGy dose. The accumulation of
these positive charges develops a built up electric field within the polymer. Some positrons,
which otherwise would have formed Ps are pulled out of this positive charge cloud and lead
to a decrease in I3 up to 100 kGy. The variation of τ3 suggests that the built up electric field
during PALS measurement do not affect the o-Ps lifetime. But this field effect is responsible
only for some electrons and positrons escaping from the positive charge cloud and decreases
the probability of Ps formation [2]. After 100kGy, the electron irradiation causes chain
session which result in enhanced bond cleavages and H2 gas evolution leading to the
formation of C=C bond structure PMMA. The presence of these C=C groups adjacent to
methyl carboxylate group unsaturated the polymer segment and hence suppresses the built up
electric field within the composite. As a result, the built up electric field is ineffective after
100 kGy and hence positron parameter depends only on free volume properties.
[1] V. Ravindrachary et al., Poly. Deg. Stab. 96 (2011) 1676-1686.
[2] Z. Q. Chen et al., J. of Radioanal. Nucl. Chem. 255 (2003) 291.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 65 OP 28 11th International Workshop on Positron and Positronium Chemistry Electron Beam Induced Microstructural Changes and Electrical
Conductivity in Bakelite Polymer RPC Detector Material -A Positron
Lifetime Study
K. V. Aneesh Kumar§, L. M. Munirathnamma, S. Ningaraju, H. B. Ravikumar
and C. Ranganathaiah
1
Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore -570 006,
India.
Resistive Plate Chambers (RPCs) [1] are being used in the study of atmospheric
neutrinos in the proposed India based Neutrino Observatory (INO) Mega Project. These
RPCs are made up of high resistive materials like glass or Bakelite due to their low cost and
excellent stable performance. However, the RPCs particularly made of Bakelite which is a
polymer undergo straining due to over exposure of direct mechanical stress, temperature, and
high energy radiation. One of the main issues is the large leakage current since the RPCs are
operated at high DC potential.
In order to understand why large leakage is current is encountered in Bakelite
detectors; we have undertaken in this study radiation induced structural modifications in
Bakelite RPC detector materials (P-120 NEMA LI-1989 Grade XXX) through free volume
quantification. The samples were exposed to electron beam of energy 8 MeV in steps of 20
kGy up to 100 kGy and characterized by Positron Annihilation Lifetime Spectroscopy
(PALS), electrical conductivity measurement and Fourier Transform Infrared spectroscopy
(FTIR)
Free volume from PALS and
conductivity are plotted and shown in
Fig.1. We observe increased in free
volume size at the lower electron doses
(20 & 40kGy) and reduced size at the
higher doses. This indicates the chain
scission followed by cross linking due to
the 8 MeV e- beam irradiation of Bakelite
RPC detector material [2]. FTIR results
revealed the scission of hydrogen bonded
phenolic groups leading to the formation Fig. 1: Variation of free volume size (Vf) and
of OH- and H+ free radicals in the lower electrical conductivity (σ) as a function of
dosages. The electrical conductivity of 40 electron dose.
kGy electron irradiated sample shows
higher value. This indicates the increased mobility of large number of OH- and H+ free
radicals produced from the cleavage of hydrogen bonded phenolic groups. The low electrical
conductivity 1.08 x10-8 (Ω m)-1 measured at 100 kGy is due to the cross linking of polymeric
chains through hydrogen bonds. The increased crosslink density and reduced ion mobility at
higher electron doses possibly reduce the leakage current and hence could be inferred as
improved performance of Bakelite RPC detector material upon e-irradiation.
[1] R. Santonico, R. Cardarelli, Nucl. Instr. Meth. 187 (1981) 377-380.
[2] K. V. Aneesh Kumar, H.B. Ravikumar, C.Ranganathaiah, J. Appl. Polym. Sci 130 (2013)
793-800.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 66 11th International Workshop on Positron and Positronium Chemistry OP 29 Positron Annihilation Spectroscopy on LiBH4 and LiBH4:LiI
Superionic Lithium Conductors
Morten Eldrup§, Didier Blanchard and Dadi Sveinbjörnsson
Department of Energy Conversion and Storage, Technical University of Denmark,
DK-4000 Roskilde, Denmark
Rechargeable lithium-ion batteries are standard in today’s consumer portable
electronics but substantial improvements are needed to achieve higher energy densities, safer
use, longer lifetimes and reduce prices to meet the demand for example in the transport sector
and storage of electrical power. Conventional Li-ion batteries use electrolytes made of
organic liquids or gels. They have high Li+ conductivity, but are flammable, causing safety
issues, and allow lithium dendrite formation at the electrode-electrolyte interface. These
dendrites cause a decrease of the cell capacity, reducing their lifetime, not to mention the
possibility of hazardous short circuits.
Lithium borohydride, LiBH4, is potentially interesting as a solid state electrolyte for Liion batteries. It consists of a lattice of Li+ cations and BH4- anions and displays high lithium
mobility, not at room temperature but above ~390 K where a transition to a high temperature
hexagonal structure occurs. This hexagonal, highly Li+ conducting phase, can be stabilized at
room temperature by lithium halides in solid solutions, in particular lithium iodide.
Considering that the Li+ conductivity is strongly influenced by the presence of Li-ion
vacancies we have carried out a series of positron lifetime measurements in order to take
advantage of the defect sensitivity of positron annihilation spectroscopy.
In coarse-grained, as-prepared LiBH4
the o-Ps lifetime shows a sharp, reversible
increase at the phase transition. In
mechanically-milled, fine-grain material
the lifetime is longer than for the asprepared material at all increasing
temperatures from 296 K to 420 K and
shows no phase transition, while a
subsequent decrease of the temperature
results in a reduction of the lifetime and an
indication of a transition, probably due to
the heat treatment at the highest
temperatures. In LiBH4 stabilized with LiI
a gradual, reversible lifetime increase is
observed in the whole temperature range.
Particularly interesting is the finding that
the variations of the positron lifetime and
+
the Li conductivity are qualitatively identical. Details of the measurements and their
interpretation will be presented at the conference.
Fig. 1. Ortho-Ps lifetime vs. temperature, increasing (filled symbols) or decreasing (open
symbols). Squares: LiBH4; triangles (first) and
diamonds (second): LiBH4 mechanically-milled;
circles: LiBH4-LiI.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 67 11th International Workshop on Positron and Positronium Chemistry OP 30 Investigation on Correlation between Defects and Conductivity of
Sb-Doped SnO2 Thin Films*
W. Mao, B. Xiong, Q. Li, Y. Liu and C. He§
Key Laboratory of Nuclear Solid Physics Huibei Province, School of Physics and
Technology, Wuhan University, Wuhan, China
Defects in undoped and antimony (Sb)-doped tin oxide (ATO) thin films fabricated via
a sol-gel method have been investigated using a slow positron beam, by which an
annihilation lineshape parameter is used to evaluate defects in the films. With increasing
calcination temperature, the resistivity for undoped films increases because of removal of
oxygen vacancies in them; however, the resistivity gradually declines for Sb-doped films
upon annealing at higher temperatures, mainly due to weakened carrier scattering with fewer
residual defects. Specifically, conductivities of 5% mol Sb doped SnO2 calcined at various
temperatures were measured as a function of temperature ranged from ~300K to ~100K. At
low temperature range from ~270K to 100K, much lower conductivity is found in the film
calcined at 400oC than that calcined at 600oC, and no prominent increase in conductivity is
found for the film calcined at 800oC. Interestingly, a strong temperature dependent
conductivity is observed in the film calcined at 400oC, however, this is not found in that
calcined at a much higher temperature of 800oC. The temperature dependent conductivity can
be well explained by variable range hopping (VRH) theory, taking account of the variations
in both defects/grain boundaries and the Sb dopant valence states in the ATO films upon
calcination at various temperatures. The results show that defects as well as dopants play an
important role in determining the conductivity of ATO films.
[1] W. Mao, B. Xiong, Y. Liu and C. He, Appl. Phys. Lett. 103 (2013) 031915.
*
This work was supported in part by the National Natural Science Foundation of China
(NSFC) under Grants No.10975108 and 11375132, and the Research Fund for the Doctoral
Program of Higher Education of China under Grant No.20090141120069.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 68 11th International Workshop on Positron and Positronium Chemistry OP 31 Novel Applications of PALS in Biophysics and Cancer Research
E. Axpe1,§, D. Merida1 , J. A. Garcia2 and F. Plazaola1
1
Department of Electricity and Electronics, University of the Basque Country UPV/EHU,
Bilbao, Spain
2
Department of Applied Physics II, University of the Basque Country UPV/EHU, Bilbao,
Spain
Free volume plays a key role in physical, diffusional and mechanical properties of
biomembranes and other biomaterials. Positron Annihilation Lifetime Spectroscopy (PALS)
is a unique technique for measuring the free volume void sizes and distributions inside these
materials. Recent studies highlight the power of PALS in biophysics and cancer research. The
goal of this presentation is to introduce and discuss the PALS results obtained in our nuclear
techniques laboratory combined with other biophysical techniques in different lipid
membranes and living cultured cancer cells [1].
[1] E. Axpe et al., PLoS ONE 9 (2014) 1.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 69 OP 32 11th International Workshop on Positron and Positronium Chemistry Positron Studies in Biopolymer Composites
A. Coveney1,2,§, F. Quero3, D. Hughes2, M. Roussenova2, P. Diaz Calderon3,
J. Enrione3, S. S. Rahatekar4, R. Richardson2 and M. A. Alam2.
1
Bristol Centre for Functional Nanomaterials, University of Bristol, Bristol, UK
2
H. H. Wills Physics Laboratory. University of Bristol, Bristol, UK
3
Biopolymer Research and Engineering Laboratory, Universidad de los Andes, Santiago,
Chile
4
Department of Aerospace Engineering, University of Bristol, Bristol, UK
Global environmental drivers have led to increased interest in the development of
degradable materials obtained from sustainable sources. Biopolymers have the potential to
fulfil this need as well as offering additional benefits such as biocompatibility and even
edibility. Furthermore, by deploying natural fillers in biopolymer matrices, the physical and
mechanical properties can be further manipulated.
Here we present the study of a biopolymer system using positron annihilation lifetime
spectroscopy (PALS). The goal is to combine free volume studies by PALS with wide angle
x-ray diffraction (WAXS), differential scanning calorimetry (DSC) and Raman deformation
measurements – amongst others – to gain insights into the mechanisms of reinforcement in
such systems.
Polymer composites of gelatin and microfibrilated bacterial cellulose are studied as a
function of composition and moisture content. Gelatin, a protein based by-product from the
meat and fishing industries has already found applications in fields ranging from tissue
engineering to food coatings [1]. The inclusion of cellulose microfibrils has been
demonstrated to influence the tensile strength and barrier properties of gelatin [2]. This work
seeks to understand this reinforcement in terms of matrix effects, in particular changes to
free-volume. Positronium lifetimes are fitted using the LT 9.1 software, with orthoPositronium (o-Ps) lifetime modelled as a continuous distribution about a mean lifetime.
[1] M. Roussenova et al., New Journal of Physics, 14 (2012) 035016.
[2] M. Fadel et al., Journal of Composite Materials, 47 (2013) 1977.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 70 OP 33 11th International Workshop on Positron and Positronium Chemistry A Study of Synthetic and Natural Dyes by the Positron Annihilation
Lifetime Spectroscopy
A. Pivtsaev§ and V. I. Razov
Far Eastern Federal University,8 Suhanova Str., Vladivostok, Russia
The purpose of this work is a study of chemical additives by the positron annihilation
lifetime spectroscopy (by the example of dyes) for the presence of carcinogenic properties.
The study considers a possibility either to confirm or disprove, on the basis of the research
data, the safety of use of actual concentrations of food dyes.
During the research annihilation spectra of synthetic food colors have been measured
(in the form they are used in food industry: main substance is dye and the rest is admixture),
demonstrating both evident carcinogenic properies: E-133, E-124, and not evident
carcinogenic properties - mutagenic: E-132, E-151, E-102 and their 10%, 5%, 2,5% and 1%
solutions; and solutions of different concentrations of natural food dye E-100 (curcumine).
Using received annihilation data time (τ3)-dye concentration charts have been plotted,
Fig.1.
From
Fig.
1,
at
concentration 5%, a conclusion
may be drawn that there is an
obvious difference in trends
between mutagenic dyes E151,
E132 and other dyes having
evident
carcinogenic
properties, and E102.
As
concentration
is
reduced from 100% to 5% the
value of long-lived time Fig. 1: Time component (τ ) – dye concentration charts.
3
component Ps (τ3) rises sharply
for mutagenic and very slowly
for carcinogenic. On further watering of solutions τ3 value rises, and in 1% solution overruns
1,0 ns practically for all of them, which transfers them in non-carcinogenic group, which is
confirmed by experiments on animals.
However in 1% solution carcinogenic properties do not disappear, they just reduce their
activity. Damage caused to the body by any carcinogens has cumulative character because
free radicals appeared due to reciprocity of carcinogen with the body do not vanish but
continue influencing, and this influence summarizes during the whole life.
Concentration increase of carcinogenic dyes leads to sharp decrease of positron (τ3)
lifetime, i.e. to increase of carcinogenic activity; as for mutagenic dyes - while concentration
increases τ3 decreases slowly, which means that carcinogenic properties will be evidently
demonstrated at the most concentrations.
All the above conclusions about the presence of carcinogenic properties in synthetic
dyes are confirmed in comparison with the natural dye - curcumine E-100.
§ e-mail:
[email protected]
Cidade de Goa, Goa, India November 9­14, 2014 71 OP 34 11th International Workshop on Positron and Positronium Chemistry Examination of a Coal by Means of Positron Annihilation Spectroscopy
C. A. Palacio1,§, F. Reyes Caballero2, W. Anwand3, J. A. Mejía1 and
S. A. Martínez Ovalle2
1
GIFAM-Grupo de investigación fundamental y aplicada en materiales, Universidad Antonio
Nariño, Tunja, Colombia.
2
FINUAS-Grupo de Física Nuclear Aplicada y Simulación, Universidad Pedagógica y
Tecnológica de Colombia, Tunja, Colombia
3
Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, POB 510 119,
01314, Dresden, Germany.
For the reactivity of the coal, the surface area or the porosity are important factors
besides of other chemical factors. There are no studies in which the nano-porosity of the coal
is linked to positron annihilation results. However, there have been studies in which the
porosity of other carbonaceous materials is related to measurements in positron annihilation.
In this work, a coal sample has been studied by means of positron annihilation
spectroscopy. The coal was obtained from Las Casitas mine (Paipa-Boyacá, Colombia). The
positron annihilation result has been related to the results obtained by means of other
spectroscopic techniques. A complete analysis is reported.
Keywords: Coal, Positron Annihilation Spectroscopy.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 72 OP 35 11th International Workshop on Positron and Positronium Chemistry Bose-Einstein Condensation of Positronium in Silica Pores
O. Morandi1,§, P. –A. Hervieux1 and G. Manfredi1
1
Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS and Université de
Strasbourg, BP 43, F-67034 Strasbourg Cedex, France
We investigate the possibility to produce a Bose-Einstein condensate made of
positronium atoms in a porous silica material containing isolated nanometric cavities. The
evolution equation of a weakly interacting positronium system is presented. The model
includes the interactions among the atoms in the condensate, the surrounding gas of
noncondensed atoms, and the pore surface. The final system is expressed by the Boltzmann
evolution equation for non-condensed particles coupled with the Gross-Pitaevskii equation
for the condensate. In particular, we focus on the estimation of the time necessary to form a
condensate containing a macroscopic fraction of the positronium atoms initially injected in
the material. The numerical simulations reveal that the condensation process is compatible
with the lifetime of ortho-positronium.
Fig. 1: Time evolution of the ratio between condensed Nc and total number of particles Nt . Particle
density 10−2 nm−3 (Tc = 66 K). Pore sizes: R = 100 nm (continuous curve), R = 200 nm (dashed curve),
R = 300 nm (dot-dashed curve). Total condensation time: t1 = 11 ns, t2 = 24 ns and t3 = 38 ns.
[1] O. Morandi, P. –A. Hervieux and G. Manfredi, Physical Review A 89 (2014) 033609.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 73 11th International Workshop on Positron and Positronium Chemistry OP 36 Cesium Loading Capacity of Iron Phosphate Glasses Studied by Positron
Annihilation Spectroscopy
S. Abhaya§, M. Premila, R. Rajaraman, G. Amarendra and C. S. Sundar
Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, INDIA
Iron phosphate glasses are proposed as potential waste matrices to immobilize high
level nuclear wastes (HLW) rich in phosphates, sulphates and alkali metal oxides. Iron
phosphate glasses with a nominal composition of 40 mol% Fe2O3:60 mol% P2O5 (IPG) is
found to have the best chemical durability, best glass forming ability and low crystallization
tendency. In this paper, we have used positron lifetime spectroscopy to follow the
microstructural evolution of open volume defects upon
doping of Cs in IPG. IPG and Cs doped IPG (with 5, 12, 18
and 35 mol% Cs2O) were prepared by mixing appropriate
quantities of Fe2O3, NH4H2PO4 and Cs2CO3 in an inert
atmosphere argon glove box, taking care to maintain an Fe/P
ratio of 0.67. The mixtures were then melted and
subsequently quenched on to SS dies to yield the respective
glasses. Positron lifetime measurements were carried out on
undoped and Cs doped IPG samples using the fast-fast lifetime
spectrometer having a time resolution of 260 ps. The undoped
IPG exhibits two lifetime components, 1 (263 ps)
corresponding to the reduced bulk lifetime and 2 (428 ps)
corresponding to the defect lifetime. As Cesium content is
increased, 1 remains constant at nearly 260 ps. However 2
shows a decrease upto 18 mol% of Cs and is seen to increase
again for higher Cs loading. However, the void intensity I2
decreases linearly from 40 to 8 % with increased Cs doping as
shown in Fig. 1. Ab-initio positron lifetime calculations based
on atomic superposition method were carried out for
Fig. 1: Variation of 1, 2 and
Fe3(P2O7)2 - the parent crystalline counterpart of IPG, with
intensity I2 with Cs doping
various defect configurations to explain the observed
in IPG.
variations in resolved lifetime components. Accordingly, the
decrease in defect intensity (I2) can be understood in terms of
depletion of the available voids or open spaces as Cesium concentration is increased.
Interestingly, decrease in 2 up to 18 mol% and subsequent increase for higher Cs content
points to local structural changes. Progressive densification is seen with increase in Cs content
[1]. Hence the initial decrease in 2 can be understood as due to increased densification of local
structure upon Cs loading, leading to shrinkage of voids. Our recent Micro Raman studies on
Cs loaded samples show drastic softening of phonon modes beyond 18 mol% of Cs [2].
Though the density continues to increase beyond 18 mol% Cs, softening of phonon modes
indicate local structural expansion, leading to increase in void size and hence increase in 2.
These results show that positron annihilation technique is a useful tool to follow the waste
loading capacities in glasses.
[1] Kitheri Joseph et al., Journal of Nuclear Materials 384 (2009) 262.
[2] M. Premila et al., manuscript under preparation.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 74 11th International Workshop on Positron and Positronium Chemistry OP 37 Spin Polarized Low-energy Positron Source
V. N. Petrov1,§, S. N. Samarin2, K. Sudarshan2, L. Pravica2, P. Guagliardo2 and
J. F. Williams2
1
2
St. Petersburg State Polytechnical University, St. Petersburg 195251, Russia
Centre for Atomic, Molecular and Surface Physics (CAMSP), School of Physics,
The University of Western Australia, Perth WA 6009, Australia
Intensity, a.u.
Extensive research in the field of surface physics depends on efficient sources and on
polarized electron detectors. The possibility of using a positron beam as a tool for the detailed
study of a surface is currently being discussed. The report presents the design of a low-energy
spin-polarized positron source at the University of Western Australia, as well as the
preliminary experimental results obtained
with its aid. It is well-known that positrons
3000
emitted from radioactive sources in the
process of beta decay, have a preferred spin
2500
positrons
electrons
direction. The positrons substantially retain
2000
their spin orientation, even after the process
of deceleration when passing through the thin
1500
film (~ 1 micron) of tungsten. This effect
allows creating a slow spin- polarized
1000
positron beam. The positron gun consists of a
500
radioactive source of positrons, a positron
0
20
40
60
80
100
decelerator (moderator) and electron optics.
The positron source is based on the
Positron energy, eV
radioactive decay of 22Na isotopes. The Fig. 1: Intensity of positrons and electrons
positrons are decelerated by using the as a function of energy of primary positrons.
polycrystalline tungsten film.
W (100) and W (100)-Fe films were studied as the samples. They were chosen due to
the fact that their magnetic and electric properties were repetitively studied by various
methods of electron spectroscopy. The figure shows the dependence of the intensity of
positrons and electrons as a function of energy of the positrons incident on the surface of
tungsten. Quite apparently, the peak corresponding to the first diffraction maximum is seen at
the energy of about 15 eV for positrons and electrons.
The magnetic properties of iron films evaporated on the tungsten surface have also been
under the investigation. The iron film got periodically magnetized in two opposite directions
during the measurements. The experiments were set in order to register the intensity of
electrons and their asymmetry. The asymmetry was calculated by the formula: A = (I+ - I-)/
(I+ + I-), where I+ and I- are the electron intensities for different directions of magnetization
of the iron film, relative to the direction of polarization of the positron beam.
Apparently, the asymmetry reaches a significant value 3% in the region of the
electronic surface resonance ~ 7 eV [1]. Analysis of the result allowed us to determine the
polarization of the positron beam. Its value was about 10%.
In the report will discuss ways to increase the polarization and intensity of the positron
beam.
[1] E. G. McRae et al. Phys. Rev. B 24 (1981) 4230.
§
e-mail: [email protected], [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 75 11th International Workshop on Positron and Positronium Chemistry OP 38 Nanoparticles Based Transparent Ceramics for Scintillation and Detection
Applications*
F. A. Selim1,2,§, I. Bartošová2,3, V. Slugeň3 and P. Husband2
1
Center for Photochemical Sciences, Bowling Green State University, Bowling Green,
OH 43403, USA
2
Department of Physics, Bowling Green State University, Bowling Green, OH 43403, USA
3
Institute of Nuclear and Physical Engineering, Faculty of Electrical Engineering and
Information Technology, Slovak University of Technology in Bratislava, Ilkovičova 3, 812 19
Bratislava, Slovak Republic
Inorganic Scintillators are important in many areas of fundamental research and
applications such as high energy physics, nuclear detection and medical diagnostics. With
great demand in such applications it is crucial to develop new efficient inorganic scintillators.
Ce doped Y3Al5O12 single crystals have been extensively studied for this purpose. However
the presence of defects and the deviation from stoichiometry have hindered its development
to efficient scintillators. Our recent positron lifetime measurements [1] on Y3Al5O12 (yttrium
aluminum garnet) single crystals has led to significant insight about defects in garnet single
crystals and revealed how they affect exciton dynamics.
Accordingly, we switch our attention to the development of YAG transparent ceramics
which may offer excellent alternative for single crystals in scintillation applications. In this
work, the latest development in nanoparticles based transparent ceramics will be discussed
with emphasis on revealing their microstructure and its effect on the optical and scintillation
properties. Positron annihilation spectroscopy (PAS) and scanning electron microscopy
(SEM) were applied to study their microstructures. Positron lifetime measurements identified
the size and character of grain boundaries and revealed the absence of voids in these YAG
transparent ceramics. The optical and scintillation properties were investigated by a variety of
optical and luminescence spectroscopies including our newly developed X-ray based
luminescence spectrometer [2] which provides a unique simple technique for luminescence
studies and direct measurement of scintillation properties not available by standard
photoluminescence and scintillation methods.
[1] F. A. Selim et al., Phys. Rev. B 88 (2013) 174102.
[2] C.R. Varney, M. A. Khamehchi, Jianfeng Ji, and F.A. Selim, Review of Scientific
Instruments 83 (2012) 103112.
*
Acknowledgements: Funding for this work was provided by the National Science
Foundation (DMR1359523 grant).
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 76 OP 39 11th International Workshop on Positron and Positronium Chemistry When Some Elementary Free Volumes in Polymers are not seen by
Positron Annihilation Experiments*
V. P. Shantarovich1,§, V. W. Gustov1, V. G. Bekeshev1, A.V. Pastukhov2,
E. V. Belousova1, I. B. Kevdina1, and M. K. Filimonov1
1
Semenov Institute of Chemical Physics Russian Academy of Sciences, Moscow, Russia
2
Nesmeyanov Institute of Organoelement Compounds, Moscow, Russia
What is the lower limit of the number density of elementary free volumes (EFV), when
PALS experiments do not detect them? Obviously, for different materials this limit can be
different and dependent on mobility of pre-localized positronium. This limit comes when
non-localized positronium is not able to find EFV before annihilation. In this study, we were
trying to find this limit. We distinguished intrinsic microporosity, typical for homogeneous
polymeric membrane materials (such as PTMSP, for example), and externally affected
porosity for heterogeneous systems (so called mixed membrane matrixes MMM). In the last
case, some new pores in the basic material are created additionally or intrinsic pores are
modified in the sites of the admixture location. Variation of concentration of the admixture
and its type in the composition change the number of externally affected EFV and their size
distribution. Correspondingly, a distance between the EFV in MMM is changed. In this way,
it is possible to come to the limit, when PALS is not able to detect some EFV, normally the
largest, though they are very effective in variation of gas permeation and sorption properties.
Nevertheless, their presence can be proved by some supplementary technique used in this
work: low temperature gas sorption (BET) [1], giving size distribution of elementary free
volumes in the range 1-60 nm. This study is further development of the recent attempts [2,3]
to determine the place of the PALS method among the others, useful in the free volume
studies. In this connection, we compare PALS and gas permeation data with the
characteristics of thermo-stimulated luminescence (TSL), namely the intensity of high
temperature component of the TSL curve, and found it very effective for the express analysis
of gas permeation. This is because so called “local rigidity” of polymer structure determines
effective size of the local free volume.
Experimental part of this work includes PALS, BET (BJH) permeation and specific
surfaces studies of MMM on the bases of polyhexafluoropropylene (PHFP) and polymer of
intrinsic micro-porosity PIM-1, filled with some metal-organic frame works. Some sorbents
(porous copolymers of divinilbenzene with rubbers) were investigated too.
Combination of PALS and BET (BJH) methods demonstrated that, for, membrane
materials and sorbents, PALS technique is the most effective in the range of micro-pores
(diameter d < 1 nm), where there is practically no alternative, and in the range of smaller
meso-pores (<3 nm), where the data can be compared with the results of BJH experimentys.
This comparison enables calculation of the number density of micropores (1019-1020g-1) and
effective diffusion coefficient of prelocalized positronium in the studied polymers: DPLPs ≈
3×10-4 cm2/s.
[1] V. P. Shantarovich , J. Polym. Sci: Part B: Polymer Physics 46 (2008) 2485.
[2] V. Shantarovich, et al., Phys. Stat. Solidi (c) 6 (2009) 2387.
[3] V. P. Shantarovich et al. Acta Physica Polonika A 125 №3 (2014).
*
Financial support of RFBR grants №12-03-00169a and 12-08-00648a is acknowledged.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 77 11th International Workshop on Positron and Positronium Chemistry Posters Cidade de Goa, Goa, India November 9­14, 2014 78 11th International Workshop on Positron and Positronium Chemistry P 1 An Experiment to Observe Positron–atom Bound States
D. A. Cooke§
1
Institute for particle physics, ETH Zurich, Zurich, Switzerland
An experiment to detect positron–atom bound states arising from charge-exchange
collisions between positronium (Ps) atoms and neutral atomic species is proposed. Although
the positron binding energies of a number of atomic species have been calculated [1], and
there is substantial evidence for positron binding to molecules [2], to date, no experimental
observation of positron–atom binding has been made.
It is planned that the experiment will use a beam–foil method [3] to generate a beam of
Ps atoms at low energies which will be intersected with a gas jet of magnesium atoms. The
energy of the Ps beam will be determined by time-tagging the positron and then measuring
the time-of-flight of each Ps atom. The reaction:
Ps + Mg → [Mg–e+] + e−,
yielding an electron below the ionization potential of Mg, made energetically possible by the
binding energy of the Mg–e+ system, will be used as a unique signal of a positron binding to
an atom. Mg was identified as the best candidate for detection using this method as the
binding energy is predicted to be > 0.4 eV and the ionization energy is 7.64 eV, so the
reaction is separated from break-up of Ps and ionization of an atomic electron.
The experiment requires few-eV Ps, so detection of the incident beam will be
inefficient. However, the requirement for ionization of an electron provides a fast stop signal
for the time-of-flight measurement, so detection of Ps atoms is only necessary for diagnostic
purposes. It is expected beam intensities of around 1 s-1 can be achieved into a 1% solid angle
beam. Timing resolution of the beam of < 5 ns is required.
[1] J. Mitroy, M. W. J. Bromley and G. G. Ryzhikh, J. Phys. B 35 (2002) R81.
[2] G. F. Gribakin, J. A. Young and C. M. Surko, Rev. Mod. Phys. 82 (2010) 2557.
[3] P. Mills and W. S. Crane, Phys. Rev. A 31 (1985) 593.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 79 11th International Workshop on Positron and Positronium Chemistry P 2 Nonlinear Dynamics of Electron–positron Clusters
G. Manfredi1,§, P. –A. Hervieux1 and F. Hass2
1
Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS and Université de
Strasbourg, BP 43, F-67034 Strasbourg Cedex
2
Departamento de Fisica, Universidade Federal do Parana, 81531-990,
Curitiba, Parana, Brazil
Electron–positron clusters are studied using a quantum hydrodynamic model that
includes Coulomb and exchange interactions. A variational Lagrangian method is used to
determine their stationary and dynamical properties. The cluster static features are validated
against existing Hartree–Fock calculations. In the linear response regime, we investigate both
dipole and monopole (breathing) modes. The dipole mode is reminiscent of the surface
plasmon mode usually observed in metal clusters. The nonlinear regime is explored by means
of numerical simulations. We show that, by exciting the cluster with a chirped laser pulse
1


E (t )  E0 g (t ) cos  0 (t  t 0 )   (t  t 0 ) 2  with slowly varying frequency (autoresonance), it is
2


possible to efficiently separate the electron and positron populations on a timescale of a few
tens of femtoseconds.
Evolution of the dipole d (left frame) and widths i (right frame) for an e–p cluster with N =100. The
excitation frequency 0 is constant and equal to the Mie frequency d and the amplitude is E0 = 0.005
au.
Evolution of the dipole d (left frame) and widths i (right frame) for an e–p cluster with N = 100. The
excitation is autoresonant with E0 = 0.005 and = −10−4 au. The dotted line on the top frame
represents, in arbitrary units, the electric field envelope g(t).
[1] G. Manfredi, P.-A. Hervieux and F. Haas, New Journal of Physics 14 (2012) 075012.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 80 P 3 11th International Workshop on Positron and Positronium Chemistry Study of the Positronium Thermalization in Porous Materials
O. Morandi1,§, P. –A. Hervieux1 and G. Manfredi1
1
Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS and Université de
Strasbourg, BP 43, F-67034 Strasbourg Cedex, France
We simulate the thermalization process of a high energetic positronium gas trapped in a
silica pore. The gas dynamics is reproduced by using a kinetic approach. Our approach
includes the two-body scattering interaction and the exchange of energy between the atoms
and the internal surface of the pore cavity. We find that the thermalization process proceeds
in two steps. The first is characterized by the formation of a quasi-equilibrium gas state with
a well-defined temperature. We estimate the characteristic time of the internal thermalization
of the gas for different atomic densities and injection energies.
We find that the thermalization time is strongly dependent on the gas density (see
figure). It is estimated to be equal to few fs for high density gases (with density of 10−2 nm−3)
and 80 ps for rarefied gases (with density of 10−5 nm−3). After having compared the results of
our simulations with some experimental results, we use our model to simulate the evolution
of the gas in a large trap maintained at a cryogenic temperature. We find that the creation of a
Bose-Einstein condensate is compatible with the ortho-positronium lifetime.
Fig. 1. Thermalization time as a function of the initial atomic density
(the density axis is in logarithmic scale).
[1] O. Morandi, P. –A. Hervieux and G. Manfredi, Eur. Phys. J. D 68(4) (2014) article :84.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 81 11th International Workshop on Positron and Positronium Chemistry P 4 Positron Nitrogen Molecule Scattering Using ro-vibrational Close Coupling
Method
T. Mukherjee1,§ and M. Mukherjee2
1
2
Physics Department, Bhairab Ganguly College, Kolkata-700056, India.
Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064, India.
Positron scattering with atom/molecule is one of the important areas of research work to
study the nature of the interaction between the sub-atomic particles. In atomic scattering
processes the interaction is between the projectile and the electrons of the target atom. But for
molecular scattering the dynamical coupling of the nuclear motion of the molecule with the
positron affects substantially the effective interaction potential. But the theoretical quantum
mechanical calculation of positron molecule scattering process becomes complicated due to
the inclusion of the nuclear coordinates. To tackle the problem some approximate methods
have been used. Among these the ro-vibrational close coupling mehod is an elaborate and
extensive way to include the rotational and vibrational motion of the nuclei in the calculation.
Earlier this method has been used to study positron hydrogen molecule scattering [1]. In the
present work we have studied positron nitrogen
molecule scattering using ro-vibrational close
coupling method in low energy region. The crucial
effect of target polarization has been included via the
positron correlation polarization potential (PCOP) [1].
The target molecule has been represented by an
elaborate wave function of nitrogen molecule. Here
we have computed the integrated total, vibrational and
rotational excitation cross sections in the energy range
from 0-10 eV. In Fig.1 we have plotted the present
total cross sections along with the theoretical results of
Fig.1. Comparison between present
Tenfen et al. [2] and the measured values by Hoffman computed integrated total cross
et. al. [3], Sueoka and Hamda [4] and Zecca et al. [5]. sections and the theoretical results of
The reason behind the variation amongst different Tenfen et. al and different measured
results and the present vibrational and rotational values for positron nitrogen molecule
excitation cross sections will be discussed and scattering.
reported at the time of conference.
[1]
[2]
[3]
[4]
[5]
§
T. Mukherjee and N. K. Sarkar, J. Phys. B 41 (2008) 125201.
W. Tenfen, et al., Phys. Rev. A 86 (2012) 042706.
K. R. Hoffman et al., Phys. Rev. A 25 (1982) 1393.
O. Sueoka and A. Hamda, J. Phys. Soc. Jpn. 62 (1993) 2669.
A. Zecca, L. Chiari, A. Sarkar, and M. Brunger, New J. Phys. 13 (2011) 115001.
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 82 P 5 11th International Workshop on Positron and Positronium Chemistry The Collision between Two Positronium (Ps) Atoms*
Hasi Ray1,2,3,§
1
Department of Physics, New Alipore College, New Alipore, Kolkata 700053, India
2
Study Center, S-1/407, B. P. Township, Kolkata 700094, India
3
National Institute of Technical Teachers’ Training and Research Kolkata, Salt lake city,
Kolkata 700106, India
When positron (e+) and positronium (Ps) interact with an atom, there are always some
possibilities of annihilation. Three different types of annihilation may occur. The direct /pickoff annihilation generally dominates when the target is a closed shell atom. The second kind
happens due to rearrangement/ exchange of electron. By electron-exchange ortho-Ps
transforms into para-Ps and annihilates, the phenomenon is known as the quenching. In open
shell atomic targets like hydrogen, alkali atom etc., the possibility of quenching is more
significant. Another types of annihilation may occur due to spin-flip caused by the spin-orbit
interaction, but the possibility is very poor. Ray [1-2] recently introduced an ab-initio and
exact static-exchange model and a new code to study the four-body Coulomb problem
exactly in the center of mass frame. The code is used to study the Ps(1s)-Ps(1s) elastic
collision. The total/integrated elastic cross section, the quenching cross section and their
conversion ratio are calculated. The conversion ratio is the parameter to measure the fraction
of total cross section transformed into para-Ps. The elastic cross section (  ) and the
quenching cross section (  q ) are defined [3] so that:
d q
2
d 3  2 1  2
1 
 f
 f
(1)
and

f f
(2)
d 4
d 16
4
Here f  and f  are the scattering amplitudes for the singlet and triplet spin-states of the two
system electrons and  represents the scattering angle. The variation of the total elastic cross
section (  ) and the quenching cross section (  q ) with the incident energy in Ps (1s)-Ps(1s)
elastic collision are presented in Fig.1. The variation of the corresponding conversion ratios
are presented in Fig.2 and are compared with the Ps-H system [4]. Detailed will be discussed
at the PPC-11.
Fig.1: The variation of  and  q . Fig. 2: The variation of conversion ratio.
[1] H. Ray, arXiv 1311:3132 (November 2013).
[2] H. Ray, Pramana (2014) in press.
[3] H. Ray and A. S. Ghosh, J. Phys. B 29 (1996) 5505. [4] H. Ray and A. S. Ghosh, J. Phys. B 31 (1998) 4427. *
§
The author is thankful to DST, Govt. of India for granting Ref.SR/WOSA/PS-13/2009.
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 83 P 6 11th International Workshop on Positron and Positronium Chemistry The Collision between Positronium (Ps) and Muonium (Mu)*
Hasi Ray1,2,3 and Rina De4,§
1
Department of Physics, New Alipore College, New Alipore, Kolkata 700053, India
2
Study Center, S-1/407, B. P. Township, Kolkata 700094, India
3
National Institute of Technical Teachers’ Training and Research Kolkata, Salt lake city,
Kolkata 700106, India
4
Department of Physics, Raja Rammohan Roy Mahavidyalaya, Radhanagar, Hoogly 712406,
India
The positrons emitted from a radioactive source into a gas at normal pressure, do not
suffer annihilation by collision with atomic electrons before they have a high probability of
capturing an electron from a gas atom to form positronium (Ps) [1]. If the captured electron
( e  ) has the opposite spin to the positron ( e  ) forming para-Ps, the lifetime towards mutual
annihilation is only about 10-10 sec; but if the spins are parallel, forming ortho-Ps, the lifetime
is much longer about 10-7 sec. The mutual annihilation of para-Ps is associated with emission
of two  -ray photons each having energy 511 Mev. Annihilation may occur due to the
exchange collision of Ps with gas atoms by which ortho-Ps transforms into para-Ps, is known
as quenching. We are interested to study quenching in Ps and muonium (Mu) collision when
both are in ground states. Mu is an exotic atom, a bound system of an antimuon (   ) and an
electron ( e  ) was discovered experimentally by Hughes [2] in 1960. We study the total
elastic cross section (  ), the quenching cross section (  q ) and the conversion ratio for
Ps(1s)-Mu(1s) collision using an exact and ab-initio static-exchange model code recently
introduced by Ray [3-4] to study a four-body Coulomb problem in the center of mass frame.
The  and  q are defined [5] so that:
d
3

f
d
4
 2

1
f
4
 2
and d
q
d

1
f
16

 f
 2
. Here f  and f  are the scattering amplitudes for the singlet and triplet spin-states of two
system electrons and  represents the scattering angle. The variation  and  q with energy
are presented in Fig.1. The corresponding conversion ratios are presented and compared with
Ps-H [5] system in Fig.2. Detailed will be discussed at the PPC-11.
Fig.1: The variation of  and  q . Fig. 2: The variation of conversion ratio.
[1] H. S. W. Massey and C.B.O.Mohr, Proc. Phys. Soc. London 67 (1954) 695.
[2] V. W. Hughes et al., Phys. Rev. Lett. 5 (1960) 63.
[3] H. Ray, Pramana (2014) in press.; [4] H. Ray, arXiv 1311:3132 (November 2013).
[5] H. Ray and A. S. Ghosh, J. Phys. B 29 (1996) 5505; 31 (1998) 4427. *
HR is thankful to DST, Govt. of India for granting Ref.SR/WOSA/PS-13/2009.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 84 P 7 11th International Workshop on Positron and Positronium Chemistry Positron Transport in a Dense Structured Media
D. G. Cocks§, W. J. Tattersall, G. Boyle and R. D. White
School of Engineering and Physical Sciences, James Cook University, Townsville, Australia
Charged particle transport encompasses a large body of applications, including medical
diagnostic techniques and treatments in which the transport of electrons, positrons and/or
positronium is the underlying physical process. While understanding of how these charged
particles interact with individual atoms (e.g. argon) or bio-molecules (e.g. water THF, THFA,
pyrimadine) has progressed significantly in the last few decades, there has been less progress
in the understanding of how many-body effects in dense media influence these particles. As
the de Broglie wavelength of the charged particles can become comparable to the mean-free
path, coherent scattering and/or resonant scattering can occur. Furthermore, earlier
experiments have shown that lifetimes of positrons or positronium atoms can be significantly
enhanced or reduced by the formation of clusters or bubbles in the bulk of the medium.
This poster presentation will discuss two approaches to deal with aspects of transport in
dense systems. The first approach makes use of the ideas of Cohen and Lekner [1], which
include the coherent scattering effects of the dense medium via the structure factor S via the
relation:
 
k'

 ( , ,  )   atomic ( 
, ) S (k  k ' ,  )
(1)
k
2
On the one hand, we use this relation to solve the Boltzmann equation, going beyond the
standard approximation by including higher order anisotropy effects, which requires the static
structure factor, and temperature as inputs. On the other hand, we include the full dynamical
structure factor directly in a Monte-Carlo simulation of particle trajectories. In both cases we
observe the effect of the medium on the transport properties of positrons in the presence of an
electric field. Comparisons between the two methods will be highlighted. The modification to
transport through inclusion of screening effects on the atomic cross-sections arising from the
dense phase will also be highlighted.
The second approach represents some of our preliminary calculations of bubble
formation in dense media. We make use of the ideas discussed by Iakubov and others [2], but
go beyond their calculations by including the structure of the medium via the pair correlator.
We show that it is possible for particles to be “captured” into a bubble due to a natural
fluctuation of the system and that the capture cross section can exhibit resonance like
structure due to the surround shell of neutral atoms or molecules in the medium. We validate
our formalism by performing explicit calculations for a Lennard-Jones system. A kinetic
theory including these physical processes will also be presented.
[1] M. Cohen and J. Lekner, Phys. Rev. 158 (1967) 305.
[2] I. Iakubov and A. Khrapak, Rep. Prog. Phys. 45 (1982) 697.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 85 11th International Workshop on Positron and Positronium Chemistry P 8 Positron Annihilation Characteristics in Polar Liquids and the FirstPrinciple Modeling
L. V. Elnikova§
Institute for Theoretical and Experimental Physics, Moscow 118218, Russian Federation
Positron annihilation spectroscopy (PAS) is a power tool to study the electronic
structure and heterogeneities of liquids [1]. By positron annihilation lifetime spectroscopy
(PALS) and the angular correlation of annihilation radiation (ACAR) technique, we propose
the new method to obtain information about the orientation of molecules of the medium at the
interface and determine the ionization potentials of complex molecular compounds by
example of water and complex organic compounds containing C–H and O–H groups
(alcohols, saturated hydrocarbons etc.) [2]. Basing on the parameters of annihilation spectra
and on the concepts of the positronium (Ps) bubble and the intratrack reactions of positron
and Ps, we determined the dimensions of cavities in which the Ps atom is localized.
Also for an illustration, we propose the first-principles calculations for the functions of
energy and polarization relating to the formation of nanoscale voids in water and acetone in
these reactions of the positron annihilation at the stage of solvated particles.
[1] V. M. Byakov, V. I.Grafutin, O.V. Koldaeva et al., J. Phys. Chem 84 (1980) 1864.
[2] V. I. Grafutin, L.V. El’nikova, O.V. Ilyukhina et al., High Energy Chemistry 47(4),
(2013) 156.
[3] L. V. El’nikova, Liquid crystals and their applications 4(46) (2013) 96.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 86 11th International Workshop on Positron and Positronium Chemistry P 9 Study of Lamellar Lyotropic Liquid Crystalline Structure by Positron
Lifetime Spectroscopy
R. Yadav1,§, K. Chandramani Singh2 and S. Roy Choudhary3
1
J. N College Madhubani, L. N. Mithila University, Darbhanga, Bihar, India
2
Sri Venketswar College, University of Delhi India
3
Department of Physics and Astrophysics, University of Delhi, India
Lamellar lyotropic liquid crystals are ordered soft materials consisting of self
organizing molecules and find application in fabricating chemical, industrial and biological
products in solutions. Wide varieties of experimental and theoretical studies of various phase
behavior of lyotropic liquid crystals exists. Still it is difficult to determine whether the
behavior observed represents that of equilibrium or some other state which may be stable or
metastable. Consequently, the experimental technique employed to investigate nanostructural
transformation in such systems must be unique. Positron life time spectroscopy has been
found to be an excellent technique [1-3].
In the present study, positron life time spectroscopy has been employed to study
swelling of lamellar structure with addition of long chain alcohol in lamellar lyotropic liquid
crystal phase of cationic surfactant/water/long chain alcohol. The study reveals the sensitivity
of positron annihilation parameters in detecting various structural transformations taking
place in such systems.
[1] P. C. Jain, Advances in Colloids and Interfacial science 54 (1995) 17.
[2] R. Yadav, K. C. Singh, S. R. Choudhary and P. C. Jain, Physica Status Solidi (c) 4 (2007)
3785-3788.
[3] G. Duplatre et al., J. Phys Chem 100 (1996) 16608.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 87 P 10 11th International Workshop on Positron and Positronium Chemistry PET in Clinical Medicine
K. Thirumurthi§
Chief-PET/CT Division, Madras Medical Mission, Mogappair, Chennai, INDIA
Positron Emission Tomography is a medical imaging technique where radioactive
‘tracer’ isotopes, which emit a positron, are injected and imaged. After traveling less than
one millimeter the positron annihilates with an electron, producing a pair of gamma ray
photons in opposite directions. The technique depends on simultaneous or ‘coincidental’
detection of this pair of photons. It is used mainly in clinical oncology, neurology and in
cardiology. PET scanning provides functional details, it is non-invasive and does not cause
discomfort to the patient. Since PET imaging lacks anatomical details, the scanning
equipment is also fitted with CT or MR scanners for concomitant image/ event registration.
The clinical useful PET tracers have short half lives and many of them require a cyclotron in
the campus for production of ultra- short-lived tracers (C-11, N-13, 0-15) for metabolic
imaging. Some tracers like F-18 (T1/2 =110 mins) are transported over short distances for
use. F-18 labeled compounds (glucose-FDG) are often used in PET imaging today. Generator
produced PET radioisotopes and ligands have been evolved for imaging and are very useful.
Newer compounds are now formulated to be labelled to F-18, Ga-68 etc. Reliable evidence is
emerging in usefulness of this technique in definite diagnosis and management of various
diseases and PET is now incorporated in imaging algorithms in clinical medicine.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 88 P 11 11th International Workshop on Positron and Positronium Chemistry Positron Trapping Studies on PVA/MPDMAPP Photochromic
Nanocomposite
Sunil G. Rathod2, V. Ravindrachary2, Blaise Lobo3, Jagadish Naik2, T. Sheela2 and
§
R. F. Bhajantri1,
1
Department of Physics, Karnatak University, Pavate Nagar, Dharwad - 580 003, India
2
Department of Physics, Mangalore University, Mangalagangotri - 574 199, India
3
Department of Physics, Karnatak Science College, Karnatak University, Dharwad 580001,
India
The organic NLO material 1-(4-methylphenyl)-3-(4- N, N, dimethyl amino phenyl)-2propen-1-one (MPDMAPP) is a π-conjugated system with donor and acceptor electrons, and
has potential application in fabricating optical devices. On doping MPDMAPP in poly(vinyl
alcohol) (PVA), it forms a charge transfer complex with PVA and emits green light (427 nm)
upon excitation with UV light, due to a photo-chromic reaction mechanism [1]. The
segmental motions in polymer based NLO composites are thought to be directly related to the
dynamical open spaces (free volume) present in amorphous regions of the polymeric
material. Positron annihilation lifetime spectroscopy (PALS) has emerged as a nondestructive chemical probe for directly determining nano-meter scale free volume holes and
their number density. Doppler broadening of the 511 keV positron annihilation peak is
characterized in terms of the S parameter, which measures the positron annihilation with low
momentum electrons of the polymeric material [2-3]. An increase in S parameter results in
increased positronium (Ps) formation, attributed to pick-off annihilation in free volume holes
of the polymeric material. The positrons have a tendency to localize in vacancy type defects
or trapped in negatively charged sites in comparatively more ordered regions, while Ps atoms
tend to be localized in the disordered parts of the semi-crystalline polymer matrix [4]. PVA is
semi-crystalline polymer and pure MPDMAPP is a highly crystalline material. The XRD
patterns of PVA/MPDMAPP composite films show essentially an amorphous microstructure. In PVA- MPDMAPP composites, MPDMAPP creates local distortions (due to
complex formation) within the PVA host material. This creates negatively charged domains
that trap the positrons, and such trapping sites are the defect regions in the polymeric
composite. The trapped positron annihilates with high-momentum electrons in its vicinity,
resulting in lowering of the S parameter.
[1] R. F. Bhajantri, V. Ravindrachary, A. Harisha, Ismayil, C. Ranganathaiah, Phys. Status
Solidi (c) 6 (2009) 2429.
[2] J. Yang et al. Chem. Phys. Lett. 597 (2014) 26.
[3] Z. Chen, et al. J. Phys. Chem. C 115 (2011)18055.
[4] V. Ravindrachary, Ismayil, Suresh P. Nayak, Dhanadeep Dutta, P. K. Pujari, Polym. Deg.
Stab. 96 (2011)1676.
*Acknowledgement: The authors are thankful to DAE-BRNS, Govt. of India for the research
project (2010/37C/7/BRNS/832) and DST, Govt. of India for the research project
(SR/FTP/PS-011/2010).
§
e-mail: [email protected], [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 89 P 12 11th International Workshop on Positron and Positronium Chemistry Amorphous Structure of the Degraded Poly (ethylene-terephthalate)
in Weathering Test
H. Hagihara§, A. Oishi, M. Kunioka, and H. Suda
Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced
Industrial Science and Technology (AIST), Tsukuba, Japan
The free-volume hole size of poly(ethylene-terephthalate) [PET] degraded in
weathering test was investigated by ortho-positronium (o-Ps) lifetime measured by means of
positron annihilation lifetime spectroscopy (PALS). With the degraded PET sample, Toray
Lumirror® S10 (50 m) which was exposed to the xenon weather meter Suga Test
Instruments SX75 (180 W/m2, BP 63 oC), the intensity of o-Ps was changed with the progress
of degradation (Fig. 1). The o-Ps lifetime (τ3) tended to be decreased with increasing
exposure time (Fig. 2, on the right hand axis, mean free-volume hole radius is also shown).
On the other hand, the gel permeation chromatography for the degraded PET implied
the chain scission by hydrolysis and the network-structure formation during the weathering
test. The increment of glass transition temperature (Tan δ) with increasing exposure time was
observed by dynamic mechanical analysis.
We previously reported that the free volume-hole size of polypropylene derivative
having hydroxyl groups was smaller than that of the non-polar analogue because of the
hydrogen bond formation [1]. The results obtained in this study indicated that inter-molecular
interaction in the amorphous part was enhanced with progress of the degradation, maybe due
to the hydrogen bond formation and/or the cross-linkage reaction. The free-volume hole size
of degraded PET observed by PALS, which was decreased with the progress of degradation,
was revealed to be helpful to evaluate the degradation of PET.
Fig. 2: The o-Ps lifetimes (τ3) for degraded
PET as a function of exposure time;
obtained at incident positron energy = 1, 5,
and 10 keV.
Fig. 1: The PALS spectra for degraded PET
at incident positron energy = 5 keV.
[1] H. Hagihara, K. Ito, and S. Kimata, Macromolecules 46 (2013) 4432–4437.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 90 P 13 11th International Workshop on Positron and Positronium Chemistry DBS Investigation on Films of Cobalt Chloride Doped PVA-PVP Blend
Preeti B. Hammannavar1, B. M. Basavarajeshwari1, R. F. Bhajantri2, V. Ravindrachary3 and
§
Blaise Lobo1,
1
Department of Physics, Karnatak Science College, Karnatak University, Dharwad 580001,
India
2
Department of Physics, Karnatak University, Pavate Nagar, Dharwad 580 003, India
3
Department of Physics, Mangalore University, Mangalagangotri 574 199, India
Cobalt chloride (CoCl2) doped polyvinylalcohol (PVA) – polyvinylpyrrolidone (PVP)
blend films (doped to different levels) were prepared by solution casting. The preparation and
characterization of these films have been described elsewhere [1]. The films were
characterized by XRD, UV-Visible spectrometry, Thermal Analysis (DSC, DTA/TGA),
FTIR and electrical measurements. In this paper, the results of Doppler Broadening
Spectroscopy (DBS) in PVA-PVP blend are discussed for the entire range of dopant (CoCl2)
concentration. The spectra were recorded using a high resolution HPGe detector, and a
program developed by us, using FORTRAN-77, was used for the extraction of line-shape
parameters. The S-parameter corresponds to annihilation of positrons whose wave-function
overlaps with those of low momentum electrons in the polymeric blend [2]. The W parameter
is a measure of positron annihilating with high momentum electrons from the crystalline
regions of the polymeric sample, including negatively charged chemical species (positron
traps). The DBS study is complemented by the XRD and DSC results.
Acknowledgement: The authors are thankful to University Grants Commission (UGC), Govt.
of India for the major research project F.38-103/2009 (SR). The HPGe X-ray detector facility
was provided by USIC, Karnatak University, Dharwad.
[1] R. V. Patil, M. R. Ranganath and Blaise Lobo AIP Conf. Proc. 1591 (2014) 183-185.
[2] Blaise Lobo, M. R. Ranganath, T. S. G. Ravi Chandran, G. Venugopal Rao, V.
Ravindrachary and S. Gopal, Phys. Rev. B 59 (1999) 13693-13698.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 91 P 14 11th International Workshop on Positron and Positronium Chemistry Computation of DBAR Parameters in Polypyrrole Incorporated PVA
Films
B. M. Basavarajeshwari1, Preeti B. Hammannavar1, M. R. Ranganath1, R. F. Bhajantri2,
V. Ravindrachary3, Manjunath Hurkadli1, Chetan Hundekar1 and Blaise Lobo1,§
1
Department of Physics, Karnatak Science College, Karnatak University, Dharwad 580001,
India
2
Department of Physics, Karnatak University, Pavate Nagar, Dharwad - 580 003, India
3
Department of Physics, Mangalore University, Mangalagangotri - 574 199, India
Flexible films of pyrrole (Py) sorbed, ferric chloride doped polyvinylalcohol (PVA)
were prepared by solution casting. Ferric chloride (FeCl3) acts both as a dopant (redox agent)
as well as an initiator for the polymerization of pyrrole, resulting in the formation of a
conducting polymeric blend, which involves a conducting component (polypyrrole; PPy) in
an insulating polymeric matrix. The preparation and characterization of these films have been
described elsewhere [1]. The films were characterized by XRD, UV-Visible spectrometry,
Thermal Analysis (DSC, DTA/TGA), FTIR and electrical measurements. In this paper, the
results of Doppler Broadening of Annihilation Radiation (DBAR) spectra (experimental) in
the entire range (from 1 wt% up to 44 wt%) of dopant (FeCl3) concentration are discussed.
The spectra were recorded using a high resolution HPGe detector, and a program in
FORTRAN-77 was developed for the extraction of line-shape parameters (S parameter, W
parameter etc). Although the calculation of S-parameter (which corresponds to annihilation
of positrons whose wave-function overlaps with those of low momentum electrons in the
polymeric blend) poses no problems [2], the calculation of W parameter using energy spectra
recorded from a single HPGe detector is complicated by enhanced background (due to effects
of the birth gamma), when sodium 22 is used as positron source. The program developed by
us involves calculation of background in 2 regions, one beyond the wing region before the
peak and the other, beyond the wing region after the 511 keV peak. The W parameter is a
measure of positron annihilating with high momentum electrons from the crystalline regions
of the polymeric sample, including traps (negatively charged defects) therein. It is noted that
the computed S parameter and W parameter reflect changes in degree of crystallinity of PPy
incorporated PVA-PVP blend, determined from XRD and DSC scans.
Acknowledgement: The authors are thankful to University Grants Commission (UGC), Govt.
of India for the major research project F.38-103/2009 (SR). The HPGe X-ray detector facility
was provided by USIC, Karnatak University, Dharwad.
[1] M R Ranganath and Blaise Lobo, Solid State Physics (India) 54 (2009) 535-536,
Proc.54th DAE SSP Symposium Dec 14-18, 2009, Ed. A.K. Rajarajan, Alka B. Garg &
G.P. Kothiyal.
[2] Blaise Lobo, M.R. Ranganath, T. S. G. Ravi Chandran, G. Venugopal Rao, V.
Ravindrachary and S. Gopal, Phys. Rev. B 59 (1999) 13693-13698.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 92 P 15 11th International Workshop on Positron and Positronium Chemistry Computation of Size of Spherical and Non-Spherical Voids in SemiCrystalline Polymeric Materials
Preeti B. Hammannavar1, Chetan B. Hundekar1, Manjunath Y. Hurkadli1, Girish Badiger1, R.
F. Bhajantri2, V. Ravindrachary3 and Blaise Lobo1,§
1
Department of Physics, Karnatak Science College, Karnatak University, Dharwad 580001,
India
2
Department of Physics, Karnatak University, Pavate Nagar, Dharwad 580001, India
3
Department of Physics, Mangalore University, Mangalagangothri 574199, India
Positron Annihilation Lifetime Spectroscopy (PALS) is a powerful tool to investigate
vacancy type defects and negatively charged chemical species in solids. The positrons from a
radioactive source like sodium-22, when injected into a solid material, annihilate at a rate
which depends on the density of electrons in the solid. In porous materials and molecular
solids, including polymeric materials, a bound state of positron and electron (positronium) is
formed, which is preferentially localized in dynamic open spaces, called free volume holes. In
this paper, we have computed the free volume hole size using a Fortran-77 program, for
spherical and non-spherical hole shapes. The Ortho-Positronium (o-Ps) life time verses cavity
size has been studied in different geometries [1]. The positron parameters extracted using
PATFIT-88 [2] has been utilized to calculate size of the free volume holes. In particular, the
longest lifetime component (τ3) and its intensity (I3) have been used, as they correspond to the
size of free volume holes and their number density respectively [3-6]. The probability of
positronium formation (P) varies linearly with I3. The computation of free volume has been
performed using PALS data of different semi-crystalline polymeric materials like
polytetrafluoroethylene (PTFE), polyvinylidenefluoride (PVDF), polyvinylalcohol (PVA) and
polyvinylalcohol – polyvinylpyrrolidone (PVA-PVP) blend. This is followed by a calculation
of trapping rates of positron and positronium in the ordered and disordered regions of the semicrystalline polymers respectively, using Goldanskii’s kinetic relations [7].
[1] B Jasinska, A E Koziol, T Goworek, J. RadioAnal. Nucl. Chem. 210(2) (1996) 617-623.
[2] P Kirkegaard, Niels Jørgen Pedersen, Morten Eldrup, Report number Risø –M-2740: Risø
National Laboratory, Denmark (1989) 132.
[3] Blaise Lobo, M. R. Ranganath, T. S. G. Ravi Chandran, G. Venugopal Rao, V.
Ravindrachary and S. Gopal, Phys. Rev. B 59 (1999) 13693-13698.
[4] G. Dlubek, A. P. Clarke, H. M. Fretwell, S. B. Dugdale and M. A. Alam, Physica Status
Solidi (a) 157(2) (1996) 351-364.
[5] S. J. Tao, J. Chem. Phys. 56 (1972) 5499-5510.
[6] M. Eldrup, D. Lightbody and N. J. Sherwood, Chem. Phys. 63 (1981) 51-58.
[7] A. V. Goldanskii, V. A. Onishuk and V. P. Shantarovich, Physica Status Solidi (a) 102
(1987) 559-564.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 93 P 16 11th International Workshop on Positron and Positronium Chemistry Change of Chemical Structure, Free Volume, and Mechanical Property of
Polyethylene Irradiated by Gamma-Ray
T. Oka1,2,§, Y. Sano2, Y. Kino2 and T. Sekine1
1
Institute for Excellence in Higher Education, Tohoku University, Sendai, Miyagi, Japan
2
Department of Chemistry, Tohoku University, Sendai, Miyagi, Japan
The chemical structure of gamma-ray irradiated organic polymers, such as polyethylene
and polypropylene, changes by main chain scission, crosslinking, and oxidation. It is well
known that the mechanical property of the sample is strongly correlated with its chemical
structure.
In this work, high density polyethylene (HDPE) with a density of 0.953 g/cm3 was
irradiated by gamma-ray with several doses in air at room temperature. The chemical
structure and the mechanical property of the samples were measured by a FT-IR spectrometer
and a tensile tester, respectively. The free volume of the samples were evaluated by the
digital positron annihilation lifetime (PAL) system [1].
Both of the tensile strength and the elongation at break for HDPE were reduced with the
irradiation, whereas the carbonyl groups,which is the indicator the oxidation, increased with
the irradiation. On the other hand, free volume size decreased with increasing the gamma-ray
irradiation dose. The change of the free volume suggests that it correlates with the
mechanical properties and the oxidation. The relationships between the change of chemical
structure and free volume, and mechanical property of low density polyethylene and
crosslinked polyethylene will be also discussed.
[1] T. Oka, Y. Sano, Y. Kino and T. Sekine, The European Physical Journal D (in press).
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 94 11th International Workshop on Positron and Positronium Chemistry P 17 Influence of Fillers on the Structural and Thermo-mechanical Properties of
Recycled High Density Polyethylene using PAS and other Techniques
D. A. Abdulmalik1,§, I. Y. Al-Qaradawi1, and N. K. Madi2
1
Mathematics and Physics Department, Qatar University, Doha, Qatar
2
Center for advanced Materials, Qatar University, Doha, Qatar
It is well known that the properties of recycled polymers are altered from their virgin
counterparts due to the presence of impurities during the recycling process. Research efforts
are under way to enhance the properties of recycled polymers to compete with virgin
materials performance and economically. In this study we examined recycled high density
polyethylene reinforced with mica, glass fiber, or graphite and various combinations of the
three representing constant fillers content of 20 wt% of the matrix. Positron annihilation
lifetime spectroscopy (PALS) has been employed to investigate the effect of the
reinforcement with the various types of fillers on the morphology of the tested composites.
The size and concentration of free-volume in the samples have been obtained. The thermomechanical properties of the composites were also investigated by means of differential
scanning calorimeter (DSC), thermogravimetric analysis (TGA) and tensile testing. The
samples were also characterized by scanning electron microscope (SEM).
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 95 11th International Workshop on Positron and Positronium Chemistry P 18 Study of the Structural and Thermo-mechanical Properties of High Density
Polyethylene composites using PAS and other Techniques
D. A. Abdulmalik1,§, I. Y. Al-Qaradawi1, and M. A. AlMaaded2
1
Mathematics and Physics Department, Qatar University, Doha, Qatar
2
Center for advanced Materials, Qatar University, Doha, Qatar
In this study, phase change composites (PCC) based on high density polyethylene
matrix (HDPE), commercial paraffin wax and expanded graphite (EG) have been examined
to investigate the effect of carbon filler on the structural and thermo-mechanical properties of
these composites. The composites were prepared with wax content up to 50 wt% and EG up
to 15 wt%. Positron annihilation spectroscopy (PAS) has been employed to probe any openvolumes in the sample’s structure after adding wax and carbon filler. The morphology of the
samples was inspected by environmental scanning electron microscope (ESEM). The
composites were also characterized using differential scanning calorimeter (DSC),
thermogravimetric analysis (TGA), and tensile testing. The combination of the used
characterization techniques helped in drawing a clear picture of the properties of the
HDPE/paraffin wax and EG blends.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 96 P 19 11th International Workshop on Positron and Positronium Chemistry A Free Volume Study on the Miscibility of PEEK/PEI Blend using Positron
Annihilation and Dynamic Mechanical Thermal Analysis*
R. Ramani, and S. Alam§
Polymer Science Division, DMSRDE, G.T. Road, Kanpur - 208 013, INDIA
The polymer Poly(ether ether ketone) (PEEK) is a high performance engineering semicrystalline thermoplastic having excellent chemical resistance and superior mechanical
properties. However, the glass transition temperature of this polymer is low (152 oC) and
hence the modulus of this material decreases at elevated temperatures. The Poly(ether imide)
(PEI) is an amorphous polymer with comparatively high Tg around 215 oC. Blending of these
two polymers combines the complimentary properties of both of them and it is now
established that PEEK and PEI are molecularly miscible in the amorphous phase [1]. With
the improved Tg, the PEEK/PEI blend is a suitable matrix resin in the preparation of high
performance composites for aerospace applications as well as for conventional spare parts in
aircraft components.
Recently, we have reported the free volume behaviour of this blend and identified that
when the PEI content in the blend is  50%, there is a high degree of miscibility due to
interlamellar segregation of PEI chains into the crystalline domains of PEEK, thus
constituting the regions of rigid amorphous fraction [2]. Alternatively, one could also
evaluate the free volume by studying the visco-elastic properties using dynamic mechanical
thermal analysis [3].
In the present study, we have performed the visco-elastic behaviour of this blend in
multi-frequency mode. Using the Williams-Landel-Ferry (WLF) relationship, master curves
were obtained at a reference temperature and the coefficients c10 and c20 were evaluated. Both
the results give similar results for the dependence of free volume on the PEI content in this
blend. A linear relationship between the relative fractional free volume (from PALS) and the
viscoelastic property (using DMTA) has been obtained using the WLF equation based on free
volume theory. The results supports the fact the free volume plays an important role in
determining the viscoelastic properties of polymer blends.
[1] G. Crevecoeur and G. Groeninckx, Macromolecules 24 (1991) 1190-1195.
[2] R. Ramani and S. Alam, J. Appl. Polym. Sci. 125 (2012) 3200-3210.
[3] A.J. Marzocca, S. Cerveny, W. Salgueiro, A. Somoza and L. Gonzalez, Phys. Rev. E 65
(2002) 021801.
*
Acknowledgements: The authors thank Prof. C. Ranganathaiah, Department of Studies in
Physics, University of Mysore, Mysore for extending the positron lifetime facility for this
work.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 97 11th International Workshop on Positron and Positronium Chemistry P 20 Positron Annihilation Spectroscopy and Orientation Study of
PMMA/MWNT
Shilpa Vijay1,§, J. K. Vijayavargiya1 and Y. K. Vijay2
1
2
Department of physics, Govt. college, Kota-324001, India
Department of physics, University of Rajasthan, Jaipur-302004, India
Positron Annihilation Spectroscopy technique utilizes the interaction between the
positron and the e- from the host material. Doppler broadening of annihilation radiation in
PMMA/MWNT, using 22Na as a positron source, were performed to study pure Poly methail
methaacrylic acid (PMMA) and doped PMMA with different concentration of MWNT
(multiwall carbon nanotube). Orientation behavior of MWNTs (0.1.0.3 and 0.5%) in PMMA
matrix has been studied using scanning electron microscopy and FT-IR spectroscopy.
Confirmation of MWNT in PMMA matrix is characterized by X-ray diffraction.
MWNT/PMMA nanocomposites have been synthesized by solution cast method. Dispersion
of MWNT in PMMA matrix has been performed by ultrasonication. SEM images show
surface morphology of MWNTs oriented in PMMA matrix. FT-IR spectra show interaction
nature of MWNT with PMMA matrix. The S–W parameter was measured for as a function of
the relative weight used in the samples. This behaviour of the S-W parameter was analysed in
terms of positron annihilation and positronium formation for the various samples. Results
show direct correlations between these parameter and the various physical characteristics of
Carbon nanotube.
[1] F. Faupel, J. Kanzow, K. Günther-Schade, C. Nagel, P. Sperr, G. Ko¨gel, Mater Sci
Forum 219 (2004) 445.
[2] C. D. Beling, C. C. Ling, C. K. Cheung, P. S. Naik, J. D. Zhang, S. Fung, Appl. Surf. Sci.
252 (2006) 3172.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 98 P 21 11th International Workshop on Positron and Positronium Chemistry Confined Water in Controlled Pore Glass CPG-10-120 Studied by Positron
Annihilation Lifetime Spectroscopy and Differential
Scanning Calorimetry
O. Šauša1,§, I. Maťko1, E. Illeková1, E. Macová2 and D. Berek2
1
Institute of Physics, Slovak Academy of Sciences, Dúbravská 9, 845 11 Bratislava, Slovakia
Polymer Institute, Slovak Academy of Sciences, Dúbravská 9, 845 41 Bratislava, Slovakia
2
Porous materials with fine size pores have perspective applications to be protective
media for storage or targeted transport of useful wettable liquids or also solids. The various
studies of these systems have revealed that numerous physical properties of such confined
liquids and probably also solids might be modified or even principally changed. Water
belongs to the most important substances in nature and is essential for the life. The
knowledge of water properties in confined systems is very important.
Recently, systematic research of confined systems associating positron annihilation
lifetime spectroscopy (PALS) and differential scanning calorimetry (DSC) methods has been
launched [1,2,3]. In the present study, the thermal behaviour of water solidified in the
controlled pore glass CPG-10-120 of mesoporous category (12,6 nm average pore size) is
investigated. The results are compared with the study of the bulk water and ice by positron
annihilation method [4].
The low-temperature evolution of various forms of free volumes in the CPG/water
composite in the wide temperature region 20-300 K was studied by PALS. The free volume
cavity sizes were determined from the positron annihilation lifetime spectra.
The DSC measurements were performed using power-compensation DSC8500 (PerkinElmer) with automatic intracooler (200 K). The encapsulated samples of 15 – 30 mg and
dynamic argon atmosphere were used.
Calorimetric measurements revealed, besides effects related to the melting or freezing
point depression of a confined liquid [5], presence of certain transitions at lower
temperatures, which could be detected only for cooling regime. An attempt of their
interpretation on basis of free volumes characterisation was done.
[1] M. Iskrová, V. Majerník, E. Illeková, O. Šauša, D. Berek, J. Krištiak, Mat. Sci. Forum
607 (2009) 235.
[2] E. Illekova, J. Krištiak, E. Macová, I. Maťko, O. Šauša, J. Therm. Anal. Calorim. 113
(2013) 187.
[3] O. Šauša, E. Illeková, J. Krištiak, D. Berek, E. Macová, J. Phys: Conf. Ser. 443 (2013)
012059.
[4] O. Šauša, M. Iskrová, B. Sláviková, V. Majerník and J. Krištiak, Mat. Sci. Forum 607
(2009) 235.
[5] M. R. Landry, Thermochimica Acta 433 (2005) 27.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 99 11th International Workshop on Positron and Positronium Chemistry P 22 PALS Study of Free Voids in Ion Exchanged Low-Silica Zeolites
S. Bosnar1,§ and D. Bosnar2
1
Division of Materials Chemistry, Ruđer Bošković Institute, Zagreb, Croatia
Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia
Zeolite materials have important applications in catalysis, ion exchange and adsorption
[1]. To optimise and improve these applications materials with desired properties should be
produced. This makes investigations of properties of zeolite materials and their synthesis
procedure an important task and structural characterisations of precursors and intermediates
during zeolite synthesis process as well as structure of the final product play very important
role. In these characterizations PALS shows itself as a very useful method. PALS results in
structural investigations of zeolite precursors show presence of voids with sizes characteristic
for zeolite secondary building units, which are formed at the beginning of the synthesis
process or even during zeolite precursor preparation. During synthesis void concentrations,
and in some cases sizes, increase to the values characteristic for the structural void sizes of
specific zeolite [2]. Zeolite porous structure beside present cations could also contain water
or other liquid or gaseous fillers. These induce changes in the sizes of the free voids inside
the zeolite structure. PALS is also here very useful method to detect these voids and changes
in their sizes connected to the amount and properties of the filler [3, 4]. In this work, some
results from current PALS investigations of influence of different cations present inside
zeolite structure on the sizes of free voids and the amount of water adsorbed will be shown.
2
[1] J. D. Sherman, Proc. Natl. Acad. Sci. USA, 96 (1999) 3471.
[2] D. Dutta, S. Chatterjee, B. N. Ganguly and K. T. Pillai, J. Appl. Phys. 98 (2005) 033509.
[3] A. M. Habrowska and E. S. Popiel, J. Appl. Phys. 62 (1987) 2419.
[4] A. Cabral-Prieto, I. García-Sosa, J. Jiménez-Becerril, M. Solache-Ríos and S. Bulbulian,
Microporous Mesoporous Mater. 69 (2004) 109.
*Acknowledgements: This work has been supported by projects at the MSES of the Republic
of Croatia 098-0982904-2953, 098-0982886-2893, 119-1191005-1021 and IAEA CRP
contract 17251.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 100 11th International Workshop on Positron and Positronium Chemistry P 23 Characterization of Contaminated Clay with Radioisotope using Positron
Annihilation Spectroscopy
S. Nishijima1,§, Y. Akiyama1 and Y. Honda2
1
Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
2
ISIR, Osaka University, Ibaraki, Osaka, Japan
After the Fukushima nuclear power plant accident, many processes have gone on to
remove the fear of residence over the residual long-lived radioisotopes. It is known that the
dominant part of radioactive Cs is kept in soil, especially in clay of silicate around
Fukushima. There is no easy way to leach it completely out of contaminated clay. There are
various kinds of clay are included in soil, and extractable level of isotopes depends on the
type of clay. Phillosilicate is a group of silicate, having periodic laminar structure composed
of silicate sheet and silicate mineral sheet. One type belonging to phillosilicate has a unit
consisting of one octahedral sheet such as aluminosilicate sandwiched with two tetrahedral
silicate sheets (2:1 clay). Cs is hard to be leached out of such clay even with strong acid,
compared to 1:1 clay because of local strong electric field and/or preferable space of defect.
Once Cs ions are extracted through ion exchange process in soil, those are to be absorbed by
2:1 clay and kept there stably. Condensation of Cs may be achieved by washing out soil.
Thus an identification of the sort of soil or clay is crucial to decide substantial
decontamination process.
Positron seems a good probe to investigate a local electronic state of the location where
Cs cations are trapped, since positron has a high mobility and easy to find the location Cs
likes. We have been measured several types of clay with positron annihilation spectroscopy
(PAS). The distinct difference between 2:1 clay and 1:1 was observed in coincidence Doppler
broadened energy spectrum and small difference was observed in there for different sort of
clay belonging to same 2:1 clay. The difference between 2:1 clay and 1:1 clay was also
observed in the lifetime spectra. If the method to characterize each kind of clay can be found
by investigating correlation between extraction rate of Cs and relevant PAS parameters, it
would be valuable in decontamination process.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 101 11th International Workshop on Positron and Positronium Chemistry P 24 Comparison Study between Energy-tunable Positron Annihilation and
Flow-type Ellipsometric Porosimetry
Kenji Ito1,§, Shigeru Yoshimoto2, Brian E. O'Rourke1 and Nagayasu Oshima1
1
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
2
Toray Research Center, Inc., Otsu
Subnanoscopic porosimetry with high sensitivity is a key tool for developing innovative
functional thin materials, useful to various applications such as gas sensors and separation
membranes. To date it has been well documented that the energy-tunable positron
annihilation technique is quite advantageous for exploring nano- and subnano-scaled total
porosity in thin films, while other sensitive adsorption porosimetry based on ellipsometry and
X-ray refractivity can only detect open porosity. In this study, we applied low-energy
positron annihilation and flow-type ellipsometric porosimetry [1] to the elucidation of
nanoscaled pores formed in silicon-oxide-backboned thin films prepared through plasma
enhanced chemical vapor deposition [2,3,4]. We discuss the consistencies and discrepancies
between the measured results for the pore characterization by both techniques with respect to
the difference in measurement principle between the two methods. A first attempt at applying
the AIST atmospheric positron-probe micro analyzer [5] combined with adsorption
porosimetery to the pore characterization is also introduced at the workshop.
[1] S. Yoshimoto, K. Ito, H. Hosomi, Y. Takai, Jpn. J. Appl. Phys. Conf. Proc., Submitted.
[2] T. Oka, K. Ito, M. Muramatsu, T. Ohdaira, R. Suzuki, and Y. Kobayashi, J. Phys. Chem.
B 110 (2006) 20172.
[3] K. Ito, T. Oka, Y. Kobayashi, R. Suzuki, and T. Ohdaira, Radiat. Phys. Chem. 76 (2007)
213.
[4] K. Ito, T. Oka, Y. Kobayashi, R. Suzuki, and T. Ohdaira, Phys. Procedia 35 (2012) 140.
[5] W. Zhou, Z. Chen, N. Oshima, K. Ito, B. E. O'Rourke, R. Kuroda, R. Suzuki, H.
Yanagishita, T. Tsutsui, A. Uedono, N. Hayashizaki, Appl. Phys. Lett. 101 (2012)
014102.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 102 11th International Workshop on Positron and Positronium Chemistry P 25 Very Low Energy Positron Scattering from W (100)
James F. Williams1,§, Sergey N. Samarin1, Kathi Sudarshan1, Vladimir N. Petrov2Oleg
M. Artamonov3, Luka Pravica1 and Paul Guagliardo1
1
Centre for Atomic, Molecular and Surface Physics (CAMSP), School of Physics,
The University of Western Australia, Perth WA 6009, Australia,
2
St. Petersburg State Polytechnical University, St. Petersburg 195251, Russia
3
Research Institute of Physics, St. Petersburg State University, St. Petersburg 199034, Russia
W
Moderator voltage (V)
We measured number of scattered positrons from W(100) surface as a function of the
moderator potential, which determines the incident positrons energy. Given the W(100)
sample has a negative work-function of about 3 eV, a positron approaching the sample
surface with the energy say 1 eV above the vacuum level will see a step-like potential and
will be reflected. When the energy of incident positrons increases up to the positron workfunction they start entering the solid and, by consequence, this reduces the reflection of
positrons from the surface. Energy dependence of the positron reflectivity at higher energies
is likely related to the density of positron states distribution above the positron work-function
level (see Fig. 1).
A low energy positron entering a solid occupies
Scattering of very low energy positrons from W(100) surface
an empty "positron" state above the vacuum level.
The spectrum of unoccupied positron states, in
Sample general, is different from the electron unoccupied
states. Energy distribution of positron states above the
E
vacuum level, beside its importance for general
knowledge of the positrons’ properties, is important
E
for the interpretation of the variable energy PALS
(Positron Annihilation Life-Time Spectroscopy) data.
Indeed, the annihilation of a positron inside a solid Fig.1. Positron reflectivity as a
follows an implantation of a positron at a certain function of energy. EW – positron
depth inside the solid. Elastic scattering of a positron work function level.
back into the vacuum is a competing channel to the
implantation. On the other hand one can expect that the probability of a positron scattering
back into the vacuum (hat is complementary to the probability to enter the solid) is sensitive
to the density of positron states at the corresponding level (these states are of course
unoccupied): the reflectivity is high where the density of states is small or where the energy
gap exists. In contrast, the reflectivity is small where the density of states is large.
Electron analogue of such an experiment is called Total current spectroscopy [1] and
used for studying unoccupied electronic states above the vacuum level.
vac
16
14
12
10
8
6
4
2
0
-2
-4
-6
16
14
12
10
8
6
4
2
0
-2
-4
-6
[1] S. Komolov, Total Current Spectroscopy of Surfaces, Gordon and Breach Science
Publishers S.A, 1992.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 103 11th International Workshop on Positron and Positronium Chemistry P 26 Probing Defects at the Buried Interfaces/Layers in Organic
Semiconductor Devices
Priya Maheshwari1, S. K. Sharma1, S. Mukherjee1, D. Dutta, K. Sudarshan, N. Padma2,
D. Bhattacharya3 and P. K. Pujari1,§
1
Radiochemistry Division, 2Technical Physics Division, 3Solid State Physics Division,
Bhabha Atomic Research Center, Mumbai, India
Analogous to conventional inorganic semiconductors, the performance of organic
semiconductors (OSC) is directly related to molecular packing, crystallinity and growth
mode. The efficiency, performance and stability of organic devices (organic field-effect
transistors (OFETs), organic photovoltaic cells, organic light emitting diodes etc.) critically
depend on the structural properties of active materials (OSC) as well as interfaces. For
instance, in OFETs, the interface between metal (source/drain) and OSC layer influences
charge carrier injection while, the gate/insulator and OSC layer interface is important for the
formation/interruption of conducting channel. The characterization of structural defects in
these films is prerequisite to achieve best possible performance of these devices. Depth
profiling defects in these films is usually carried out by layer by layer removal, thus,
damaging the sample. In this regards, beam based positron annihilation spectroscopy (PAS)
is a sensitive technique to probe defects in layers and buries interfaces non-destructively.
Depth profiling using slow positron beam has been carried out in OSC thin films to
probe defects especially structural disorder at the bulk layers and buried interfaces. Defect
profile has been obtained by Doppler broadened annihilation S-parameter as a function of
positron incidence energy. The structural defects and homogeneity has been examined for the
films grown on different substrates and growth parameters. In the context of OFETs,
molecular packing and disorder at the interface between OSC and the dielectric has been
investigated for films grown on self assembled monolayer modified dielectric substrates. The
S-parameter profile and positron lifetimes at different depths have been correlated with the
variation of morphology and molecular packing of the film due to modification of the
substrate surface. The results are correlated with the obtained field effect mobility of the
charges. The study on OSC devices using slow positron beam has open an avenue in organic
electronic industry for the characterization of defects in devices non-destructively.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 104 P 27 11th International Workshop on Positron and Positronium Chemistry Metal-Semiconductor Interfaces Investigated by Positron
Annihilation Spectroscopy
Abdulnasser S. Saleh§
Department of Physics, University of Benghazi, Benghazi, Libya
Variable-energy positron annihilation spectroscopy has been applied to study interfaces
in Al/Si, Au/Si and Au/GaAs structures. A computational modeling by ROYPROF program
was used to analyze Doppler broadening results in order to determine kinds of regions that
positrons are likely to sample [1]. In all fittings, the interfaces are considered 1 nm thick and
act as an absorbing sink for positrons diffusing towards them and may be regarded as
negatively charged. Internal electric fields were found to influence positrons diffusing to the
interfaces. The results of these theoretical fitting models have clearly demonstrated the
sensitivity of interfaces in these attempts.
[1] A. S. Saleh, J. W. Taylor and P. C. Rice-Evans, Applied Surface Science 149 (1999) 87.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 105 11th International Workshop on Positron and Positronium Chemistry P 28 Development of a Method to Measure the Positron Diffusion Constants in
Metals by the Observation of Positronium Negative Ions
T. Suzuki§, H. Terabe, S. Iida, T. Yamashita and Y. Nagashima
Department of Physics, Tokyo University of Science, Japan
We have developed a new method to measure the positron diffusion constants in metals
by the observation of positronium negative ions (Ps-). Ps- emission fractions from the sample
surfaces are used to obtain the fractions of positrons which return to the surfaces. The γ rays
emitted from self-annihilation of accelerated Ps- are Doppler-shifted and the peaks due to the
ions are isolated from 511 keV peaks on the γ ray energy spectra. Thus one can clearly
distinguish the Ps- components from pair-annihilation of positrons occurred in the bulk or on
the surface and self-annihilation of positronium atoms. This method has been enabled by
recent studies of efficient production of Ps- using alkali-metal coating on metal surfaces [1,
2].
Figure 1 shows the γ ray energy spectrum for a polycrystalline tungsten sample. It was
annealed at 1500 ˚C in situ and then coated with Na before the measurement. The peak at 526
keV is attributed to the self-annihilation of Ps-. Figure 2 shows the Ps- fractions plotted
against the positron incident energies. The positron diffusion constant has been obtained by
fitting the positron diffusion model [3].
We are planning systematic measurements of diffusion constants for the metals which
emit Ps- after alkali-metal coating.
Positron incident energy : 8.0 keV
1.0
Ps fraction fPs- (%)
0.04
0.02
0.01
0
500
0.8
Positron diffusion constant
2
D = (0.22 ± 0.03) cm /s
0.6
0.4
-
Counts / s
0.03
510
520
530
0.2
0.0
0
540
Photon energy (keV)
Fig.1 : γ ray energy spectrum for the
positron incident energy of 8.0 keV.
5
10
15
20
25
Positron incident energy Ee+ (keV)
Fig.2 : Ps- fractions plotted against
incident positron energies.
[1] Y. Nagashima, T. Hakodate, A. Miyamoto, K. Michishio, New. J. Phys. 10 (2008)
123029.
[2] H. Terabe, K. Michishio, T. Tachibana, Y. Nagashima, New. J. Phys. 14 (2012) 015003.
[3] T. Suzuki, H. Terabe, S. Iida, T. Yamashita, Y. Nagashima, to be published in
Nucl. Instr. and Meth. in Phys. Res. B.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 106 11th International Workshop on Positron and Positronium Chemistry P 29 Positron Annihilation in Layer High Temperature Superconductors
A. Paiziev§
Institute Ion-Plasma&Laser Technologies Uzbek Academy of Science, Tashkent, Uzbekistan
To investigate quantum dimensional effects (QDE) in thin quantum dimensional films
need to use monochromatic positron beams (necessity of high vacuum, clearing of a surface,
maintenance of uniformity of a film on thickness etc). To overcome this troubles we offer to
study monocrystalline high temperature superconductors (HTSC) with layered electronic
structure when conducting layers Cu-O(1) alternate with non-conducting La-O(2) layers
along crystalline axis c (for example La-Ba-Cu-O, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O, Ti-Ba-(Ca)Cu-O compounds). As conducting layers have strictly identical thickness (about inter plane
distance 2.4 Å) such substances are very convenient to study dimensional effects by positron
isotope methods. It is shown that main contribution in anisotropy of ADAP spectra is
connected with positron annihilation in conductive Cu-O(1) layer. To describe behavior of
conductive electrons in Cu-O(1) layer the 2D model of free Fermi gas was used. In
transversal direction states of electrons are described in model one-dimensional potential
well. It is shown that in transversal direction ADAP spectra have a several “plateau”
corresponding to position of allowed electron states and parabola like form of ADAP spectra
in longitudinal direction.
In this case expression for a longitudinal and perpendicular component of ADAP spectra for
the positron captured on the lowest level (n=1) is:
R  4(2 )
4
sin 2 P d / 2

( P d ) 2 ( P d ) 2  (2 ) 2

2


P2
RII  1  2 y 2 2 
 KF   / d 
1
2
(1)
It is shown that the main contribution in ADAP spectra give the first quantum state of
electrons in Cu-O(1) layer (n=1) and the contribution more highly laying states in ADAP has
a maximum for emission angles of annihilation photons corresponding to position on discrete
quantum states in conducting layer. With increasing of number of a subzone their
contribution to R|| decreases. The cutting angle of total spectrum ADAP corresponds to
number of a subzone in which the positron at the moment positron annihilation (in this case n
=1) is located. According to (1) ADAP for R shows presence of "oscillating talk" for greater
momentums and periodically repeating features in the shape "plateau" which one corresponds
to positions of subzones in momentum space. For parallel component ADAP spectra take
place “cutting” of R|| component of ADAP spectra (1). It shows that HWHM of curve R for
captured states of positron is more appropriate for free positron state. This circumstance is
probably connected with restricted movement of a positron in a cross direction in the
potential well that lead to increase of collision frequency of a positron with walls of potential
well and leads to additional broadening of annihilation lines in comparison to a case free
annihilation. Note, that both in the first, and in the second cases are observed weak oscillation
R1 on a tail of spectrum ADAP with periodicity 4  for dimensionless parameter  =p1d.
Same behavior of curve ADAP takes place and in case of annihilation for free positron states.
It is shown that FWHM for R|| more narrow than for R . It has been shown that for
superconductivity are responsible valence electrons of oxygen O(1) ions in Cu-O(1) layer,
which concentration, anyway, less than electronic density of bulk metal. On the other hand
FWHM for R do not depend on a parameter of superconductive layer.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 107 11th International Workshop on Positron and Positronium Chemistry P 30 Positron Interactions with Quartz Materials*
J. D. Van Horn §, F. Wu and Y. C. Jean
1
Department of Chemistry, University of Missouri-Kansas City, Kansas City, USA
Both amorphous and crystalline quartz materials are of significant industrial and
scientific value due to their variety of properties used in a wide range of applications. The
interaction of positron and positronium with these materials has been of interest to a number
of researchers over the years and continues to be so [1, 2]. Amorphous quartz offers good
resistance to radiation damage, and crystalline quartz offers a unique and well-defined
crystalline lattice for studies of the positron interactions with these types of material. Here we
present our comparisons of amorphous, fused quartz versus crystalline quartz.
In Doppler-broadening energy spectra (DBES) measurements of quartz samples there is
a significant and differential interaction of the positron with fused and crystalline material
(see Fig. 1). Generally, this result points to the
0.5
difference in the greater defect amount in the
Fused Quartz
0.49
amorphous quartz versus the crystalline
material possessing an ordered array, and
0.48
presumably much less defect.
0.47
In bulk positron annihilation lifetime
S
0.46
spectroscopy (PALS) measurements, the
differences in amorphous versus crystalline
0.45
Crystalline Quartz
quartz can be deconvoluted into the lifetimes
0.44
and intensities. Regarding observed lifetimes
0.43
the defect volumes appear to be similarly sized
0
5
10
15
20
25
30
(cf.  3), but with a requisite larger I3 related to
Positron Incident Energy (kev)
the defect amount in the amorphous material. Also of interest is the difference in 2; we Fig. 1: DBES data for fused (top) and
associate this lifetime with the ortho-Ps crystalline quartz (bottom) expressed as a
shape-parameter (S).
annihilation in the lattice of the materials.
Table 1. Bulk PALS lifetimes and intensities for amorphous and crystalline quartz. The
number in parentheses represents the calculated error in the last significant digit reported.
Sample
Fused quartz
Cryst.
quartz
 1 (ns, fixed
[2])
0.156
0.156
 2 (ns)
 3 (ns)
I1 (%)
I2 (%)
I3 (%)
Var.
0.53(1)
0.329(2)
1.594(7)
1.50(3)
27.2(3)
33.5(7)
22.4(3)
62.8(6)
50.4(4)
3.7(1)
1.042
1.055
[1] M. L. Chithambo, et al., Radiation Measurements 46 (2011) 310.
[2] H. Saito and T. Hyodo, Phys. Rev. Lett. 90 (2003) 193401.
*
We thank Prof. James Murowchick (UMKC Geosciences) for technical assistance and the
University of Missouri Research Board for partial funding of this work.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 108 P 31 11th International Workshop on Positron and Positronium Chemistry Defects Study on Magnetic Fluorescent Fe3O4/ZnSe Nanocomposites by
Positron Annihilation Spectroscopy
A. Roychowdhury1,§, S. Kumar2 and D. Das1,*
1
UGC-DAE Consortium for Scientific Research, KC, III/LB-8, Kolkata-98, India
2
Department of Physics, Jadavpur University, Jadavpur, Kolkata-32, India
Nanocomoposites (NCs) comprising magnetic and fluorescent materials are of current
interest due to their potential bio-medical applications [1]. Defects present in a NC affect its
magnetic as well as optical properties [2]. In the present work, defects present in Fe3O4/ZnSe
NCs prepared by a chemical route are characterized by positron annihilation spectroscopy
(PAS). Positron annihilation
lifetime data of the NCs were
deconvoluted
with
three
lifetime (1, 2 and 3)
components. The shortest
lifetime (1) is assigned to an
admixture of lifetimes due to
annihilation
at
monovacancies
that
are
predominantly present at the
surface and grain boundaries of
the NCs and annihilation with
free electrons residing there
[2]. The intermediate lifetime
component (2) has been
assigned to trapping of
positrons at the intersection of Fig. 1: Variation of positron annihilation parameters τ , τ , I ,
1 2 1
three or more grain boundaries I2, τav and Doppler broadening S-parameter with magnetite
e.g. triple junctions.
The concentration.
longest lifetime (3) has been
assigned to formation of orthopositronium at larger voids in the NCs. As shown in Fig1(a),
both 1 and 2 decrease as magnetite concentration in the NCs increases that is explained as
due to flow of free electrons from magnetite to annihilation sites reducing the average
electron density. The variation of the intensity patterns I1 and I2 (Fig. 1(b)) with concentration
of magnetite indicates dependence of defect densities on concentration of the constituents.
The variation of the mean lifetime (av) and Dopper broadening (S) parameter with
concentration of magnetite in the NCs (Fig 1(c) & 1(d) respectively) indicates that average
defect density in the NCs steadily decreases with increase in Fe3O4 concentration implying
that majority of the defects are located in the fluorescent (ZnSe) component.
[1] H. Kim et al., J. Am. Chem. Soc. 127 (2005) 544.
[2] A. Roychowdhury and D. Das et al., J. Phys. Chem. Solids 74 (2013) 811.
§
*
e-mail: [email protected]
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 109 P 32 11th International Workshop on Positron and Positronium Chemistry Electronic Properties of Transition Metals and Alloys by Positron
Annihilation Spectroscopy
E. P. Prokopev§, V. I. Grafutin
SRC "Kurchatov Institute", Federal State Institution "State Scientific Center of the Russian
Federation - Institute of Theoretical and Experimental Physics." FGBI "SSC RF - ITEP"
Moscow, Russia
We have studied electronic and defect structures of a number of pure metals and their
alloys using positron annihilation spectroscopy [1-3]. To elucidate the effect of the electronic
structure on the macroscopic properties of pure metals, we have compared the reference data
on the electronic structure with the melting point of these metals.
For transition metals, we observed correlation between the melting point and the
number of unpaired electrons. The more unpaired electrons correspond to a higher melting
point, while there is no correlation with the total number of d-electrons. So copper (3delectrons), palladium (4d-electrons), gold (5d- electrons) with completely filled d-shell
electrons have lowest temperature in their ranks. Emphasis is placed on technetium, tungsten
and rhenium. In case of technetium, different references give different configuration of the
outer electron shell (4d65s1 or 4d55s2). In our opinion, the correct configuration will be with
6-d electrons. Following similar reasoning, tungsten outer shell electronic configuration
should be 4f145d56s1, while for rhenium it should be 4f145d66s1. We assumed that the
unpaired d-electrons characterize the tendency of metals to form covalent bonds which are
stronger than metallic bonds. The process of formation of such bonds is likely cause for the
increase in the melting point with increasing number of unpaired d-electrons. We have not
found any mention of this effect in the literature. These effects may also explain the presence
of possible modified ductile-brittle transition of Ioffe type in structural materials (metals and
alloys) under neutron irradiation at elevated temperatures [2].
[1] V.I. Grafutin, E.P. Prokopiev et al., Nuclear physics 74, N 2 (2011)195-206.
[2] V.I. Grafutin, E.P. Prokopev et al., Plant Laboratory 75, N 6 (2009) 27-36.
[3] V.I. Grafutin, Yu.F. Kozlov et al., Modern scientific research and innovation.
October, (2012). http://web.snauka.ru/wp-content/uploads/2012/10/
snauka_prokop_paper.pdf
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 110 11th International Workshop on Positron and Positronium Chemistry P 33 PAS Study of Zr-2.5%Nb Alloy Irradiated by Ar9+ Heavy Ions
Aruna Devi1, Ranjini Menon2, Priya Maheshwari3, S. Neogy1, P. Y. Nabhiraj2, P. K. Pujari3
and D. Srivastava1,§
1
Material science Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India.
2
Variable Energy Cyclotron Centre, 11AF Bidhannagar, Kolkata 700064, India.
3
Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India.
S-parameter
Zr2.5%Nb alloy is used as pressure tube material in pressurized heavy water reactor
(PHWR) due to low neutron absorption cross-section, high resistance to corrosion, irradiation
stability and mechanical properties. However, the high radiation environment may lead to
radiation induced damage resulting in the appearance of defects, creep and growth of the tube
that influence the mechanical properties
of the material. Positron annihilation
Mean implantation depth (nm)
710
77
448
234
spectroscopy (PAS) is a well established
0
1.025
technique to probe defects in materials.
The ability of positron to get localized in
1.020
low
electron
density
regions
1.015
(defects/open volumes) helps in probing
1.010
atomic order defects in materials with
sensitivity in the range of a few ppm.
1.005
Defect study has been carried out in Zr1.000
2.5%Nb alloys irradiated with 315 keV
Ar9+ ions with fluence varying from
0.995
3.1x1015 to 4.17x1016 ions/cm2. The
Unirradiated sample
0.990
Irradiated 1 (3.1x10 ions/cm )
defect distribution has been estimated
0.985
Irradiated 2 (4.17x10 ions/cm )
using
TRIM
calculation.
The
conventional PAS technique provides
0
5
10
15
20
Positron energy (keV)
bulk information about the material,
therefore, slow positron beam has been
Fig 1: The S-parameter profile in unirradiated and
used for defect depth profiling in the
irradiated alloys
irradiated alloys. Doppler broadening
measurement has been carried out in the positron incidence energy range 0.2-22 keV. The Sparameter (Figure 1) shows the increasing trend at lower depths indicating the presence of an
oxide layer on the alloy surface. There is significant increase in S-parameter in the irradiated
samples at a depth corresponding to the range of Ar9+ ions in the material, consistent with
TRIM calculation (100-300 nm), indicating the presence of large number of defects in
irradiated samples. The S-parameter is also seen to increase with the increase in fluence. The
SW analysis revealed the presence of similar type of defects in the samples irradiated at
different fluences. Therefore, the increase in S-parameter can be related to the increase in
defect concentration with the fluence.
15
16
§
2
2
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 111 11th International Workshop on Positron and Positronium Chemistry P 34 Study of Doppler Broadening in Neutron Irradiated ADS Related
Materials using Positron Annihilation Spectroscopy (PAS)
Naresh Chejara1,§, S. K. Gupta1, H. S. Palsania1, Aruna Bharti1, Narender Jakhar1, Dalpat
Meena1, Subhash Chandra1, Subodh Shrivatav1 and Y. K. Vijay2
1
High Energy Nuclear Physics Lab. (A.D.S. Programme) Department of Physics, University
of Rajasthan, Jaipur
2
V.G.U. Jagatpura, Jaipur
S-parameter
Doppler broadening measurements
0.90
for radiation damages by neutrons up
0.88
to 10 MeV in elements Al, Cu and
0.86
composite material Brass has been
Al
carried out using Positron Annihilation
Cu
0.84
Brass
Spectroscopy (PAS). These samples
0.82
has been irradiated by 5.0 Ci Am+Be
0.80
neutron source for different time
periods ranging from 24 hours to 120
0.78
hours in order to obtain different
0.76
0
20
40
60
80
100
120
neutron fluency. The available neutron
Irradiation Time (Hours)
5
flux at irradiated position was 3.3×10
Fig. 1 : Variation of S-parameters n/cm2/sec. A positron source Na22 of
strength 35 mCi was used and subsequently S and W parameters has been calculated for
Doppler Broadening using PAS. SEM measurements have also taken for the surface study of
these materials. SEM measurement shows substantial changes in the surface of the materials
after the irradiation.
S. No.
Material
1.
2.
3.
4.
5.
6.
7.
8.
9.
Al
Al
Al
Cu
Cu
Cu
Brass
Brass
Brass
Irradiation
Time(Hours)
24
120
24
120
24
120
S –parameter
0.8932±0.0064
0.8780±0.0062
0.8822±0.0065
0.7884±0.0042
0.8029±0.0044
0.7936±0.0043
0.7639±0.0042
0.7744±0.0043
0.7701±0.0045
W -parameter
WW+
0.0036±0.0003 0.0055±0.0005
0.0016±0.0002 0.0034±0.0005
0.0005±0.0001 0.0014±0.0003
0.0014±0.0002 0.0034±0.0003
0.0002±0.00005 0.0012±0.0002
0.0001±0.00004 0.0017±0.0002
0.0035±0.0002 0.0043±0.0003
0.0004±0.0001 0.0032±0.0003
0.0048±0.0003 0.0056±0.0004
Table 1: Calculated values of S and W parameters for Doppler broadening of annihilation peaks for
materials (before and after irradiation).
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 112 P 35 11th International Workshop on Positron and Positronium Chemistry Investigation of Helium Implanted RAFM Steel by Positron Beam Doppler
Broadening Spectroscopy
R. Renjith§, C. David, R. Rajaraman, B. K. Panigrahi and G. Amarendra
Indira Gandhi Center for Atomic Research, Kalpakkam, India
Reduced Activation Ferritic Martensitic (RAFM) steels are one of the prime candidates
for core structural materials of future fission and fusion reactors, due to their high resistance
against radiation induced swelling, helium embrittlement and attractive high temperature
mechanical properties. India Specific Reduced Activation Ferritic Martensitic (INRAFM)
steel is a 9Cr-1.4W-0.06Ta-V steel, has been developed for Indian Lead Lithium Ceramic
Breeder Test Blanket Module (LLCB TBM) in ITER [1]. The radiation tolerance of RAFM
steels under fusion environments stems from the presence of large number of trapping sites
such as dislocations, lath boundaries, and precipitates [2]. These prevent the agglomeration of
helium atoms into clusters to cause material degradation. The studies reported here are aimed
at evaluating the interactions of helium atoms with irradiation induced vacancy type defects.
INRAFM steels were implanted with 130 keV He+ ions to a fluence of 1×1016 ions/cm2
at room temperature. The samples were characterized by variable energy slow positron
Doppler broadening spectroscopy. The defect sensitive positron line shape S-parameter
shows a higher value in implanted sample as compared to the non implanted sample, which
indicate the presence of irradiation induced vacancy type defects. The implanted samples are
annealed at various temperatures to investigate thermal stability and clustering of heliumvacancy defect complexes, leading to the formation of helium bubbles. Doppler S-parameter
has shown distinct changes corresponding to different annealing stages occurring at different
temperatures. Detailed results with VEPFIT [3] analysis of the experimental data will be
presented.
[1] K. Laha, S. Saroja, A. Moitra, R. Sandhya, M. D. Mathew, T. Jayakumar and E. Rajendra
Kumar, Journal of Nuclear Materials 439 (2013) 41.
[2] Akihiko Kimura, Materials Transactions 46 (2005) 394.
[3] A. van Veen, H. Schut, M. Clement, J. M. M. de Nijs, A. Kruseman, M. R. Ijpma,
Applied Surface Science 85 (1995) 216.
§
e-mail: renjitrm @igcar.gov.in
Cidade de Goa, Goa, India November 9­14, 2014 113 11th International Workshop on Positron and Positronium Chemistry P 36 Defect Studies in Large Samples using Photon Induced Positron
Annihilation (PIPA) Spectroscopy
K. Sudarshan1, D. Dutta1, Priya Maheshwari1, S. Mukherjee1, S. K. Jha2, D. Srivastava3
and P. K. Pujari1,§
1
Radiochemistry Division, 2Atomic Fuels Division, 3Materials Science Division
Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India
Low implantation depth of positrons from isotope sources limits the size of the
sample for positron annihilation spectroscopic studies. A photon induced positron
annihilation spectroscopic method (PIPA), where positrons are produced in situ via pair
production processes upon incidence of high energy gamma rays on the sample, is an
alternative method to study defects in larger samples. The size of the samples that can be
studied using this method is limited by the attenuation of annihilation gamma-ray. A
PIPA facility is developed at the Folded Tandem Ion Accelerator (FOTIA) facility,
BARC [1]. Possibility of using prompt gamma-rays produced in nuclear reactions 27Al
(1H,γ)28Si and 19F(1H,γ)16O were examined. The reaction 19F(1H,γ)16O provided higher
photon flux. The particular nuclear reaction was also preferred due to high energy of the
gamma-rays involved, resulting in the high positron yield/pair production cross section.
The Doppler broadening of annihilation radiation measurements have been carried
out in cold worked zircaloy-2 samples and tungsten inert gas welded stainless steel
samples for the defect studies. The sizes of the samples were roughly 5cm5cm0.5cm.
The collimation of the photon beam was 2.5cm2.5cm to cover larger area in the sample.
The S-parameter in all the samples has been evaluated. Measured S-parameter, which is a
measure of defect concentration, was well correlated with the residual stress in the cold
worked zircaloy samples and welding parameters in TIG welded stainless steel samples.
The PIPA setup and results of our measurements in large samples will be discussed.
[1] P.K. Pujari et al., Nucl. Instr. Meth. B 270 (2012) 128.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 114 P 37 11th International Workshop on Positron and Positronium Chemistry Development of a Vertical, Slow Positron Beamline Facility at AIST
and Application to the Study of Liquids
Brian E. O’Rourke1,§, Nagayasu Oshima1, Atsushi Kinomura1 and
Ryoichi Suzuki1
1
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki
305-8568, Japan
We report on the development of a new positron beamline facility at AIST [1]. Positrons
are generated by the 70MeV electron beam from the AIST electron accelerator and are
magnetically guided to the experimental room. The positrons can be guided into either of two
separate beamports both of which are arranged vertically, i.e. positrons are incident on
horizontally mounted samples from above. Both beamports contain a beam chopping and
pulse bunching apparatus for high resolution positron annihilation lifetime spectroscopy
(PALS). The first port uses an unfocussed beam and is suitable for PALS and Doppler
broadening of annihilation radiation (DBAR) measurements with large (>10 mm) samples.
The second beamline contains a brightness enhancement apparatus using a transmission type
remoderator in a similar design to the existing AIST positron probe microanalyzer (PPMA)
[2]. As samples can be loaded horizontally, it is possible to study liquids on both beamports,
which until now has not been possible using our existing horizontal beam. In the contribution
we will describe the new beamline and our preliminary measurements on liquid samples.
[1] B. E. O’Rourke, N. Oshima, A. Kinomura, T. Ohdaira and R. Suzuki, Mat. Sci. Forum
733 (2013) 285.
[2] N. Oshima, R. Suzuki, T. Ohdaira, A. Kinomura, T. Narumi, A. Uedono and M. Fujinami,
J. of Appl. Phys. 103 (2008) 094916.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 115 11th International Workshop on Positron and Positronium Chemistry P 38 Design of a Pulsed Positron Beam at Trombay
S. Mukherjee1, S. K. Sharma1, Priya Maheshwari1, S. K. Gupta2 and P. K. Pujari1,§
1
Radiochemistry Division, 2 Ion Accelerator Development Division, Bhabha Atomic Research
Centre, Mumbai 400085.
We present here the design of a pulsed beam setup to deliver narrow time width pulses
to a sample for positron annihilation lifetime spectroscopic measurements. The major
constituents of the setup will include- 22Na radioactive source and moderator assembly, E×B
deflector for filtering out high energy positron and gamma rays, chopper-prebuncher-buncher
assembly for time bunching of the slow positrons. In the ExB section, the crossed electric and
magnetic field (axial) guides the slow positrons through an off-centered hole in a 25 mm
thick tungsten block. This arrangement will have better energy resolution (~ 3%) as
compared to the conventional bent beam setup. We have used curved plates instead of
parallel plates to minimize the radial distortion of the positron beam. The dimensions of the
designed plate are (i) 250 mm long (ii) 90 and 60 mm diameter for outer cylinder and inner
cylinder, respectively. The initial beam will be time bunched to 2.5 ns FWHM pulses using a
reflection type chopper which will be made of three tungsten meshes separated by alumina
insulators. The middle mesh will be fed a 37.5 MHz square wave. The prebuncher is a double
gap buncher consisting of two concentric cylinders. A 37.5 MHz RF is fed to the inner tube.
The two bunching gaps, defined by the edges of the inner cylinder, are separated by a
distance corresponding to the length (125 mm) travelled by positrons in half of the time
period of the RF (250 eV, 37.5 MHz). The main buncher was simulated using CST
Microwave Studio. It is designed as a quarter wave resonator with base frequency of 150
MHz with a Q value of 2100. Positron trajectories were simulated in the buncher cavity and
the effect of- (a) beam size (b) energy spread (c) angular spread on final pulse width is
simulated. Effect of sample bias and the drift tube bias is also monitored. The conventional
design of the quarter wave resonator will have the inner tube cantilevered at one end. To
prevent the sagging of the inner tube, we have supported the inner conductor using a
dielectric material support. The change in the resonant frequency is compensated by a
conducting plunger. The incident beam energy can be varied either by negatively biasing the
sample (compared to the moderator) or by a post-bunching accelerator.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 116 P 39 11th International Workshop on Positron and Positronium Chemistry Development of a Solar Spectrum Monitor using Coloured LEDs and
Arduino for Studying Celestial Positronium
A. Halder1, and N. N. Mondal1,2,§
1
Department of Computer Science & Electronics, Batanagar Institute of Engineering
Management and Science, Kolkata, West Bengal, India.
2
Department of Physics, Indian Institute of Engineering, Science & Technology, Kolkata,
West Bengal, India.
Living creatures can sustain only in the third planet of the solar system and maximum
energies consumed by it are being received from the Sun. Hence solar energy play important
role to our lives and the nature. In order to study the celestial positronium (Ps), the
development of a solar spectrum monitor (SSM) is important. Using the various coloured
(VIBGYOR) light emitting diodes (LED) and Arduino the SSM will be constructed. Arduino
is a tool for the interfacing of data to a computer from physical parameters such as sound,
light etc. Arduino is based on Atmel's ATMEGA8, ATMEGA328, ATMEGA168 micro
controllers etc.
The Arduino (Fig.1a) board gets its input i.e. analogue signals or external parameters
such as light. These signals are then digitized in the board and displayed via output devices
such as monitor. Data is transferred to the computer via USB cables and recorded using
external software. This data is now displayed or stored for further use. A typical spectrum of
red LED of this system is depicted in Fig.( 1b). The source of black body radiation is a fusion
(p-p reaction) in which positron (e+) are emitting and form Ps (e+e-) which can decay into
even/odd number of gamma rays. Those gamma-rays have a crucial role in order to produce
solar spectrum. By monitoring and characterizing the coloured spectra celestial Ps will be
detected that inferred the present, past and future of the astrophysical phenomena. Details of
this detector and analysed data will be presented in the conference.
Fig.1 (a). Arduino electronics, is used as
an computer interface for data taking
and analysis.
§
Fig. 1(b): Solar spectrum obtained by the
Red LED in presence of Sunlight (left)
and corresponding background without
Sunlight (right).
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 117 11th International Workshop on Positron and Positronium Chemistry P 40 A Triple Coincidence PALS Setup Based on Fast Pulse Digitizers*
D. Bosnar1,§, B. Đurđević1 and S. Bosnar2
1
Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia
2
Division of Materials Chemistry, Ruđer Bošković Institute, Zagreb
We assembled a positron annihilation lifetime spectroscopy system that consists of
three BaF2 detectors with XP2020URQ PMTs and which are coupled to a DRS4 evaluation
board [1] with four input channels. The board has a variable sampling rate for the channels in
the interval 0.7-5 GS/s and collects 1024 sampling points for each channel. Algorithms for
determining timing and energy from recorded signal pulses were developed in Root software
[2]. The constant fraction method was used to determine timing with the fraction varied until
obtaining the best time resolution. The obtained time resolution was 145 ps using only
gamma rays from photopeak and 153 ps using Compton gamma rays and gamma rays from
photopeak, with a 60Co source and maximum sampling rate of 5GS/s. In order to extend the
time window to 500 ns for triple coincidence measurements of zeolite samples, a sampling
rate of 2 GS/s was used. The obtained time resolution with this sampling rate and with a 60Co
source was 154 ps using gamma rays from photopeak and 185 ps using Compton gamma rays
and gamma rays from photopeak. These time resolutions depend slightly on the applied
energy cut. Integration of signal pulses in the whole recorded time range was used for energy
determination and it clearly allows separation of gammas in the photopeak and Compton
gammas in both cases.
One can perform standard PALS measurements, choosing 1.28 MeV gamma as a start
signal in one detector and 0.51 MeV gamma as a stop signal in the other detector. Triple
coincidence lifetime measurements can be done by demanding coincidences among 1.28
MeV gamma (start signal) in one detector and two annihilation gammas, from positronium
decay, (stop signal) in the remaining detectors. The setup is very suitable for direct
determination of positronium three gamma annihilation which is of special interest for
studying various porous materials [3,4,5]. It also demonstrates possible benefits of PALS
system based on fast digitizers. The results of measurements of selected zeolite samples will
be presented.
[1]
[2]
[3]
[4]
[5]
www.psi.ch/drs/evaluation-board
root.cern.ch
Y. Kobayshi et al., Rad. Phys. Chem. 76 (2007) 224.
Zs. Kajcsos et al., Rad. Phys. Chem. 76 (2007) 231.
S. H. Huang et al., Rad. Phys. Chem. 81 (2912) 791.
*
Acknowledgements: This work has been supported by projects at the MSES of the Republic
of Croatia 098-0982904-2953, 098-0982886-2893, 119-1191005-1021 and IAEA CRP
contract 17251.
§
e-mail: [email protected]
Cidade de Goa, Goa, India November 9­14, 2014 118 11th International Workshop on Positron and Positronium Chemistry Author Index Abdel-Hady E. E.
Abdel-Hamed M. O.
Abdulmalik D. A.
Abhaya S.
Adachi S.
Aghion S.
Akiyama Y.
Alam M. Ashraf
Alam S.
AlMaaded M.A.
Al-Qaradawi I.Y.
Amarendra G.
Anwand W.
Artamonov Oleg M.
Arutyunov N.Yu.
Asai S.
Assaf B. A.
Axpe E.
42
42
95, 96
74
53
41
21, 101
5, 23, 40, 70
59, 97
96
95, 96
20, 59, 74, 113
7, 29, 36, 72
103
50
53
27
69
Badiger Girish
Barbiellini B.
Bartošová I.
Basavarajeshwari B. M.
Basu Sandip
Beavis P.
Bekeshev V. G.
Belousova E. V.
Berek D.
Bhajantri R. F.
93
27
45, 76
91, 92
22
5, 40
77
77
99
56, 60, 65, 89,
91, 92, 93
112
104
67
16, 58
100, 118
100, 118
85
24, 41
7, 29, 36, 64
3, 55
Bharti Aruna
Bhattacharya D.
Blanchard Didier
Błażewicz A.
Bosnar D.
Bosnar S.
Boyle G.
Brusa R. S.
Butterling M.
Byakov V. M.
Caballero F. Reyes
Calderon P. Diaz
Cassidy D. B.
Ceeh H.
Chandra Subhash
Chandrappa H.
Checchetto R.
Chejara Naresh
Chen H.
Chirayath V. Anto
Choudhary S. Roy
Cocks D.G.
Comini P.
Cooke D. A.
Coveney A.
Cowan T.E.
Cyriac Jincemon
Das D.
David C.
De Rina
Deshpande S. K.
Devi Aruna
Dománková M.
Duplâtre G.
Đurđević B.
Dutta D.
Ebisawa N.
Egger W.
Eldrup Morten
Elnikova L. V.
Elsayed M.
Emtsev V. V.
Enrione J.
Faupel F.
Fedus K.
Feldblyum Jeremy I.
Ferragut R.
Fiedler F.
Filimonov M. K.
72
70
13
15
112
56
41
112
19
20
87
85
52
79
5, 70
7, 29, 36
35
109
113
84
32
111
45
3
118
26, 32, 104,
114
11
9
67
86
50
50
70
9
54
26
12, 41
29
77
Cidade de Goa, Goa, India November 9­14, 2014 119 11th International Workshop on Positron and Positronium Chemistry Fukaya Y.
18
Gaikwad P. V.
Ganguly Bichitra Nandi
Garcia J. A.
Gidley David W.
Gigl T.
Gorgol M.
Goworek J.
Grafutin V.I.
Guagliardo P.
Gupta S. K.
Gupta S. K.
Gupta S. K.
Guruswamy
Gustov V. W.
49
10
69
26
15
16
16
110
75, 103
63
112
116
65
77
Hagihara H.
Halder A.
Hammannavar Preeti B.
Harms S.
Hasegawa M.
Hass F.
Haumann M.
He C.
Hebbar Vidyashree
Heiman D.
Herold C.
Hervieux P. –A.
Hirade T.
Honda Y.
Horn J. D. Van
Hugenschmidt C.
Hughes D.
Hundekar Chetan
Hurkadli Manjunath
Husband P.
Hyodo T.
90
117
91, 92, 93
9
11
80
15
25, 68
60
27
15
52, 73, 80, 81
33
21, 101
19, 108
15
5, 40, 70
92, 93
92, 93
76
18
Ichimiya A.
Iida S.
Illeková E.
Imirzian James
Inoue K.
Ishida A.
Ismyail
Ito Kenji
Jakhar Narender
Jaworowski M. R.
Jean Y.C.
Jha S. K.
Joglekar P.V.
Jungmann M.
Kai Takeshi
Kalarikkal Nandakumar
Karbowski A.
Karwasz G. P.
Kawamura Y.
Kawasuso A.
Kempe M.
Kessler C.
Kevdina I. B.
Kierys A.
Kino Y.
Kinomura Atsushi
Kobayashi T.
Kobayashi Y.
Koschine T.
Kostenko M.G.
Koymen A. R.
Kozlovski V. V.
Krause-Rehberg R.
Kršjak V.
Kshirsagar A.
Kulikov L.A.
Kumar K.V. Aneesh
Kumar S.
Kunioka M.
Kuriplach J.
Leuenberger Bruno-H
Li Q.
Lim Z. H.
Liu Ming
Liu Y.
18
106
99
26
11
53
65
102
112
19
19, 108
46, 114
27
7
37
35
54
54
14
18
29
50
77
16
43, 44, 94
115
53
11
9
64
27
50
7, 29, 36, 50
47
49
3
66
109
90
4
5
68
27
26
68
Cidade de Goa, Goa, India November 9­14, 2014 120 11th International Workshop on Positron and Positronium Chemistry Lobo Blaise
56, 60, 89, 91,
92, 93
Macová E.
Madhu P. K.
Madi N. K.
Maekawa M.
Maheshwari Priya
99
32
95
18
32, 49, 104,
111, 114, 116
73, 80, 81
25, 68
99
26
2
112
72
111
69
41
18
51
42
42
117
73, 81
82
32, 46, 49,
104, 114, 116
82
7
66
Manfredi G.
Mao W.
Maťko I.
Matzger Adam J.
Maurer Frans H.J.
Meena Dalpat
Mejía J. A.
Menon Ranjini
Merida D.
Miotello A.
Mochizuki I.
Mohallem J. R.
Mohamed Aya H.
Mohamed Hamdy F. M.
Mondal N. N.
Morandi O.
Mukherjee M.
Mukherjee S.
Mukherjee T.
Müller A.
Munirathnamma L. M.
Nabhiraj P. Y.
Nagai Y.
Nagashima Y.
Nagumo K.
Naik Jagadish
Namba T.
Nambissan P.M.G.
Natarajan V.
Neogy S.
Ningaraju S.
Nishijima S.
Oganesyan G. A.
Ohrt C.
Oishi A.
Oka T.
O'Rourke Brian E.
Oshima N.
Ovalle S. A. Martínez
Padma N.
Paiziev A.
Palacio C. A.
Palsania H.S.
Panigrahi B. K.
Pasang T.
Pastukhov A. V.
Patil Pushkar N.
Patri M.
Perfiliev Yu. D.
Petriska M.
Petrov V. N.
Pivtsaev A.
Plazaola F.
Poveda L.
Pravica L.
Premila M.
Prokopev E.P.
Pujari P.K.
Quero F.
Rahatekar S. S.
Rahul M. T.
Rajaraman R.
Ramachandran R.
Raje N.
Ramani R.
Ranganath M. R.
Ranganathaiah C.
Rath S. K.
Rathod Sunil G.
Rätzke K.
Ravelli L.
Ravikumar H. B.
111
11
17, 106
11
60, 89
53
35, 60
63
111
66
21, 101
50
9
90
44, 94
102, 115
28, 102, 115
72
104
107
72
112
113
57
77
41
39
3
47
75, 103
71
69
51
75, 103
74
110
32, 39, 46, 49,
63, 65, 104,
111, 114, 116
70
70
35
62, 74, 113
59
32
59, 97
92
34, 57, 66
39
56, 89
9
9
66
Cidade de Goa, Goa, India November 9­14, 2014 121 11th International Workshop on Positron and Positronium Chemistry Ravindrachary V.
Ray Hasi
Razov V. I.
Reiner M.
Rempel A. A.
Renjith R.
Richardson R.
Roussenova M. V.
Roychowdhury A.
Sabelová V.
Sagar Rohan S.
Saify M. T.
Saito H.
Saleh Abdulnasser. S.
Samarin S.N.
Sankar S.
Sano Y.
Sanyal D.
Šauša O.
Schönweiz A.
Sekine T.
Selim F. A.
Selvakumar S.
Semba T.
Shantarovich V. P.
Sharma S. K.
Shastry K.
Sheela T.
Shibuya K.
Shidara T.
Shimizu Y.
Shrivatav Subodh
Singh K. Chandramani
Sinha V.
Sivaji K.
Sivaniah Easan
Sivasankari J.
Slugeň V.
Srivastava D.
Stepanov P.S.
Stepanov S.V.
56, 60, 65, 89,
91, 92, 93
83, 84
71
15
64
113
70
5, 23, 40, 70
109
Stolarz D.
Suda H.
Sudarshan K.
47
65
46
14
105
75, 103
48
44, 94
61
99
15
44, 94
76
48, 62
48
77
32, 46, 49, 63,
104, 116
27
60, 89
14
18
11
112
87
46
48, 62
5
48
45, 47, 76
31, 111, 114
55
3, 36, 55
Tang Xiuqin
Tattersall W. J.
Tedeschi Concetta
Terabe H.
Thirumurthi K.
Toyama T.
Tydda M.
Sundar C. S.
Suzuki Ryoichi
Suzuki T.
Sveinbjörnsson Dadi
Swain A.
Ubbink Job
Uedono A.
Ukai Masatoshi
25
85
5
106
88
11
58
5
48
37
Valeeva A. A.
Vallery Richard S.
Vijay Shilpa
Vijay Y. K.
Vijayavargiya J. K.
64
26
98
98, 112
98
Wada K.
Wagner A.
Watanabe Ritsuko
Weiss A. H.
White R. D.
Williams J. F.
Wong-Foy Antek G.
Wu F.
18
7, 29, 36
37
27
85
75, 103
26
108
Xiong B
Yadav R.
Yamaji T.
Yamashita T.
Yokoya Akinari
54
90
32, 39, 49, 63,
75, 103, 104,
114
6, 62, 74
115
106
67
5, 40
25, 68
87
53
43, 106
37
Cidade de Goa, Goa, India November 9­14, 2014 122 11th International Workshop on Positron and Positronium Chemistry Yoshimoto Shigeru
Zaleski R.
Zaluzhnyi A. G.
102
Zgardzińska B
Zhang W.
Zvezhinskiy D. S.
16
55
58
19
3, 36
Cidade de Goa, Goa, India November 9­14, 2014 123 

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