pptx

This work is supported by JSPS KAKENHI
Grant Number 15K13478 (Started from Apr. 2015)
方向感度をもつ暗黒物質検出器の開発をめざした
異方性を有するシンチレータ開発の検討
黒澤俊介A, B, 関谷洋之C, 村上力輝斗A, 庄子育宏A, 大橋雄二A,
鎌田圭B, 横田有為B, 吉川彰A, B
東北大金研A, 東北大NICHeB, 東大宇宙線研C
2015年9月28日大阪市立大学
日本物理学会2015年秋季大会 28aSJ-10
Total 17 pages!
DAMA’s report
Directional response
with MeV alpha particles
“Estimated” quenching factor @ 5keV
~30% difference
40~50% difference
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
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In case of stilbene crystal
P.H. Heckmann et al.,Z. Phys. 162 (1961) 122
Directional response
with MeV alpha particles
HS et al., Physics Letters B 571 (2003) 132
Measured quenching factor@40keV
only 7 % difference
24% difference
θ
Only 7%
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
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To go beyond the NC-n wall
• Directional detectors must aim at <10-48 cm2
arXiv:1307.5458 J.Billard et al.
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
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Although “direction” is not detected directly…
it’s a direction-sensitive detector
• How much ZnOW4 is necessary in Kamioka?
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
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Expected “diurnal modulation”
• Assuming 7% difference @5keV
• Including atmospheric n & DSNB BG 10 tons x 1000 days exposure!
c.f. Proton decay
22.5 ktons x 6000 days
c axis // North-South
c axis // East-West
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
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Started to prepare (10 tons of) ZnWO4!
• 2 x 2 x 2 mm3 crystal made by Czochralski process
• At Tohoku University
• A 2mm cubic crystal was cut and polished.
2.0 mm
0.2 mm
2.0 mm
To discern the
direction of the crystal
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
7
Crystal structure of ZnWO4
• Monoclinic crystal system
Schofield et al., Acta Crystallographica, Section B:
Structural Science (1997) 53, p102-p112
Lattice type
P
Space group name P 2/c
Space group number 13
Setting number
1
a [Å]
b[Å]
c[Å]
α [deg]
β [deg]
γ [deg]
4.69060
5.71820
4.92690
90.0000
90.6210
90.0000
Almost cubic!
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
8
Simulated Laue patterns
• X-ray irradiated from each axes of ZnWO4
c-axis
b-axis
日本物理学会2015年秋季大会大阪市立大学
a-axis
28aSJ-10
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Actual Laue pattern
• X-ray generator: RIGAKU RAD-IIC with Hamamatsu CCD
– 25kV, 30mA, Target：Cu
– exposure：240ns
• Distance between CCD
and ZnWO4:4cm
c-axis
X-rays
This plane is really perpendicular to c-axis!
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
10
Actual Laue patterns
• ~a axis
• ~b axis
b-axis
X-rays
a-axis
X-rays
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
11
Setup with PMT
• Hamamtsu R7600U-200 UBA PMT
– QE 25%@480n
• For fixed crystal position, Teflon + Al
mounter were attached to the PMT
ZnWO4
Paper Black tape
241Am
ZnWO4
Reflector/mounter
10 mm
optical grease
Oken 6262A
R7600U-200
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
12
Reproducibility check 1
• From ~a axis direction, “attach – remove – attach” cycled
• Both 59.5keV peak and 5.5MeV positions are same.
59.5keV X-ray
5.5MeV a
Temperature 24.1-24.2oC
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
13
Reproducibility check 2
• From ~a axis direction, but the other side of the crystal
• Both 59.5keV peak and 5.5MeV positions are same.
59.5keV X-ray
5.5MeV a
Temperature 24.1-24.2oC
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
14
Main result
• From ~a axis direction, ~b axis direction, and c axis direction
• ~12% difference in 5.5MeV a peaks, while 59.5keV peaks are same.
59.5keV X-ray
c axis
5.5MeV a
~b axis
~a axis
Temperature 24.1-24.2oC
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
15
Summary
• Directional response of ZnWO4 was confirmed.
– 12% [email protected] with sys. error
– Surface lattice defect affects?
• More perfect crystal has smaller directional response?
To Do
•
•
•
•
Evaluation with another samples of the crystal
Intrinsic background checks
Neutron beam test
Prepare 10 tons of ZnOW4
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
16
For larger crystals
• At research lab. on advanced crystal engineering, IMR, Tohoku University
• Many Czochralski machines for 3inch-size crystal.
– ~ 10kg x 1000 = 10 tons?
– It takes 2 weeks to make one.
• Optimization for ZnWO4 is underway.
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
17
Extra Slides
日本物理学会2015年秋季大会大阪市立大学
28aSJ-10
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Scintillation wavelength
• Scintillation wavelength was measure with 241Am (5.5MeV a)
– Spectrometer: Edinburgh Instrument FLS920
• Scintillation mechanism
– Charge transfer emission
• Peak emission @480nm
– There is a reproducible sharp
structure around 450nm
– Under investigation
c.f. Grabmaier IEEE TNS 31 (1984 ) 372
Hiroyuki Sekiya
CYGNUS2015
Occidental College
June 2 2015
19
Scintillation waveform
• Decay constant :10msec
References
Oscilloscope Tektronix TDS 3034B
Fitted function f = A1exp(-t/τ1) + C
τ1: 10 μsec
• Grabmaier IEEE TNS 31 (1984 ) 372
– 21.8 ms
• Holl et al., IEEE TNS 35, (1988) 105
– 20.0 ms
• Shkulkova et al., IEEE TNS 56 (2009) 994
– 700 ns & 7,000 ns & 25,000 ns
• Depends on each crystal?
– Lattice Defect affects?
– Temperature dependence?
– Will be investigated
Hiroyuki Sekiya
CYGNUS2015
Occidental College
June 2 2015
20
Setup for spectral measurement
preamp
ORTEC 113
C=1000pF
shaper
ORTEC 572A
Shaping time: 10 msec
MCA
AMPTEK8000A
• Will be tested with FADC
Hiroyuki Sekiya
CYGNUS2015
Occidental College
June 2 2015
21
Summary of what we did so far
• Scintillation wavelength: peak ~480nm
• Scintillation decay time: ~10ms
– There are differences between previous studies.
– Lattice defect affects?
– Light yield must be checked.
• Directional response was confirmed.
– 12% [email protected]
– Lattice defect affects?
with sys. error
• More perfect crystal has smaller directional response?
Hiroyuki Sekiya
CYGNUS2015
Occidental College
June 2 2015
22
To do
• Evaluation with another samples of the crystal
• Light yields check with gamma rays.
– 23% of NaI
Holl et al., IEEE TNS 35, (1988) 105
• Intrinsic background checks
• Temperature dependence of LY.
– F. Cappella et al., Eur. Phys. J. C (2013) 73:2276
– Directional respose remains?
• Neutron beam test
• Prepare 10 tons of ZnOW4
Hiroyuki Sekiya
CYGNUS2015
Occidental College
June 2 2015
23
For larger crystals
• At research lab. on advanced crystal engineering, IMR, Tohoku University
• Many Czochralski machines that
can make 3inch-size crystal.
– ~ 10kg x 1000 = 10 tons?
– It takes 2 weeks to make one.
• Optimization for ZnWO4 is
underway.
Hiroyuki Sekiya
CYGNUS2015
Occidental College
June 2 2015
24
For Low BG crystal
• In Japan, a consortium for low BG techniques was organized by
KAKENHI budget (Grants-in-Aid for Scientific Research, MEXT)
http://www.lowbg.org
• ~15M$ for 5 years
• With PICO-LON and CANDLES
– Low BG crystal technologies are
being developed.
Hiroyuki Sekiya
CYGNUS2015
Occidental College
June 2 2015
25

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