0度(p,p’)による 28SiのM1励起に関する研究

The (p,p’) experiment at 0o
at RCNP
9th April Osaka Univ.
Osaka Univ. RCNP
Hiroaki MATSUBARA
April 05 @ iThemba labs.
Collaborators for E249
Osaka U. RCNP
Osaka U. Dept. of Phys.
Univ. of Witwatersrand
CNS Univ. of Tokyo
Kyoto U. Dept. of Phys.
A. Tamii, K. Fujita, N. Hashimoto, K. Hatanaka,
M. Itoh, K. Nakanishi, Y. Sakemi, Y. Shimbara,
Y. Shimizu, Y. Tameshige
T. Adachi, Y. Fujita
J. Carter
T. Kawabata
H. Sakaguchi, M. Yosoi, J. Zenihiro
iThemba LABs
H.Fujita, F.D. Smit
Gent Univ.
L.A. Popescu
April 05 @ iThemba labs.
RCNP : overview
2. RING Cyclotron
Accelerated
up to Ep = 400 MeV
1. AVF Cyclotron
WS : High-precision spectrograph
N0 : Neutron TOF (100m)
EN&ES : Unstable nuclei (Heavy ions)
Accelerated
up to Ep = 80 MeV
April 05 @ iThemba labs.
Introduction
• The configuration mixing is an interesting
subject in the study of nuclear structure.
• Through the study of M1 excitations on
0+ T=0 nuclei, we can learn a lot.
• Light nucleus is easier to be calculated, e. g.
sd-shell one.
24Mg, 28Si, 32S
April 05 @ iThemba labs.
Quenching problems
• Less strength is observed than predicted with sum rule.
GT sum rule :
 0 | [Y , Y ] | 0  3( N  Z )
60 → 90% of the strength is observed.
T.Wakasa et al., PRC55(1997)2909 (p,n) reaction
How about M1 strengths?
 , 
Common with GT
Quenching is observed in T=0,1 M1 strengths in 28Si.
N. Anantaraman et al.,PRL52(1984)1409
Almost no quenching is observed in 24,26Mg, 28Si, 32S.
G.M. Crawley et al.,RPC39(1989)311
Improvement of the data quality is required.
April 05 @ iThemba labs.
Experimental Setup (@RCNP WS course)
Under focus mode
As a beam spot monitor
in the vertical direction
Q1 F.C.
Intensity : 3 ~ 8 nA
Target : natSi (1.9 mg/cm2)
April 05 @ iThemba labs.
Procedure of the beam tuning
• Achromatic transport mode
~40keV (FWHM) : Au(p,p0) at 8°
• Halo free beam tuning at 0°
(achromatic mode)
• Dispersion matching
(faint beam method)
~3mm (FWHM) on the target : beam spot size
It took about 2 days for beam tuning.
April 05 @ iThemba labs.
Sieve slit calibration
~ for the better vertical scattering angler resolution ~
   2   2 Around 0 deg, angel resolution is sensitive to both θ and φ.
48mm
2mmφ
18mm
58Ni(p,p
58Ni(p,p
16°GR
) at
16°GR
0) 0at
April 05 @ iThemba labs.
Before calibrations
+4.0%
F.C.
Y : Vertical position [mm]
+1.0%
+2.5%
Common scaling
Θ : Horizontal scattering angle [deg]
April 05 @ iThemba labs.
Y : Vertical position [mm]
Procedure for calibration
Projected
Gaussian fitting
Θ : Horizontal scattering angle [deg]
Each positions are obtained.
April 05 @ iThemba labs.
After calibrations
Horizontal:
Δθ= 0.15 deg
F.C.
φ:
Vertical :
Δφ= 0.5 deg at Ex = 6 MeV.
0.8 deg at Ex = 20 MeV.
ΔΘ = 0.5 ~ 0.8 [deg]
φ:
φ:
(at the target)
April 05 @ iThemba labs.
Horizontal plane (X-plane) correction
Y : The vertical position [mm]
Θ : Horizontal scattering angle [deg]
～for a better energy resolution～
X : The horizontal position [mm]
X : The horizontal position [mm]
Before calibrations
Curving and broadened
April 05 @ iThemba labs.
X-THETA correction
Small region is projected to X-axis.
Gaussian fitting
Projected to X-axis
Another region is
selected and projected.
Gaussian fitting
The curving shapes are
represented numerically.
April 05 @ iThemba labs.
The progress of the energy resolution
Ex = 11.45MeV ;1
+
20keV
April 05 @ iThemba labs.
Background subtraction (I)
True events
rotated
projection
φ:
Backgraound
Y : The vertical position [mm]
This rotation corresponds to move the VDC
to the Y focal plane.
April 05 @ iThemba labs.
Background subtraction (II)
Uniform BKG
April 05 @ iThemba labs.
A high quality spectrum
preliminary
April 05 @ iThemba labs.
G.M. Crawley et al, PRC39(1989)311, at Orsay
2000
1500
500
Present data
preliminary
April 05 @ iThemba labs.
The Differential Cross Section
OXBASH parameter from A. Willis et al., PRC 43(1991)5
preliminary
April 05 @ iThemba labs.
Strength distributions
B(σ) (μn2)
Ep = 200 MeV
M1 states only
B(σ) (μn2)
All strengths are normalized
by the data of Crawley at 11.45 MeV.
preliminary
Ep = 160 MeV
preliminary
Ep = 295 MeV
Excitation Energy (MeV)
M1 + unknown states
M1 + unknown states
April 05 @ iThemba labs.
E249 : data
These spectra were obtained in the E249 experiment.
targets:
0°2.5°4.5°
28Si ◎ ◎ ◎
48Ca ◎ ◎ ◎
64Ni ◎ ◎ ◎
12C
○ ○ ○
Mylar ○ ○ ○
13CH2 ○ －－
24Mg ○ －－
26Mg ○ －－
40Ca ○ －－
90Zr △ －－
1.9 mg/cm2 (natural)
1.9 mg/cm2
4.7 mg/cm2
1.1 mg/cm2
1.0 mg/cm2
0.7 mg/cm2
1.8 mg/cm2
1.6 mg/cm2
13 mg/cm2
1.0 mg/cm2
○... measured,
◎... good statistics,
△... poor statistics, －... not measured
April 05 @ iThemba labs.
Summary
• The (p,p’) experiments at forward angles were carried out at
WS course, RCNP.
• High quality data were obtained.
• We realized
under-focus mode (scattering angle : 0.5~0.8 deg)
dispersion matching (excitation energy : ~20 keV)
in the (p,p’) measurement at 0 degrees.
• Background was subtracted reasonably.
• The cross sections of both IS and IV type were compared with
DWBA calculations.
• The strength distributions were compared with other data.
April 05 @ iThemba labs.
Future
• Jπ assignments of each peak
• Extraction of M1 strengths and their
distributions
• Next beam time
– At finite angles
– Data for further calibrations
April 05 @ iThemba labs.

Download Report