The (p,p

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The (p,p) experiment at 0o at RCNP
9th April Osaka Univ.

• Osaka Univ. RCNP Hiroaki MATSUBARA

April 05 _at_ iThemba labs.
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Collaborators for E249

• Tamii, K. Fujita, N. Hashimoto, K. Hatanaka,
• M. Itoh, K. Nakanishi, Y. Sakemi, Y. Shimbara,
• Y. Shimizu, Y. Tameshige

Osaka U. RCNP
Osaka U. Dept. of Phys.
T. Adachi, Y. Fujita
J. Carter
Univ. of Witwatersrand
CNS Univ. of Tokyo
T. Kawabata
H. Sakaguchi, M. Yosoi, J. Zenihiro
Kyoto U. Dept. of Phys.
H.Fujita, F.D. Smit
iThemba LABs
L.A. Popescu
Gent Univ.
April 05 _at_ iThemba labs.
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RCNP overview
2. RING Cyclotron
Accelerated up to Ep 400 MeV
1. AVF Cyclotron
WS High-precision spectrograph N0
Neutron TOF (100m) ENES Unstable nuclei
(Heavy ions)
Accelerated up to Ep 80 MeV
April 05 _at_ iThemba labs.
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Introduction

• The configuration mixing is an interesting
  subject in the study of nuclear structure.
• Through the study of M1 excitations on
• 0 T0 nuclei, we can learn a lot.
• Light nucleus is easier to be calculated, e. g.
  sd-shell one.

24Mg, 28Si, 32S
April 05 _at_ iThemba labs.
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Quenching problems

• Less strength is observed than predicted with
  sum rule.

GT sum rule
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 T0,1 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 _at_ iThemba labs.
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Experimental Setup (_at_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 _at_ iThemba labs.
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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 _at_ iThemba labs.
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Sieve slit calibration
for the better vertical scattering angler
resolution
Around 0 deg, angel resolution is sensitive to
both ? and f.
April 05 _at_ iThemba labs.
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Before calibrations
4.0
1.0
2.5
Y Vertical position mm
Common scaling
T Horizontal scattering angle deg
April 05 _at_ iThemba labs.
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Procedure for calibration
Projected
Y Vertical position mm
Gaussian fitting
T Horizontal scattering angle deg
Each positions are obtained.
April 05 _at_ iThemba labs.
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After calibrations
Horizontal ?? 0.15 deg Vertical ?f 0.5
deg at Ex 6 MeV. 0.8 deg at Ex 20
MeV.
f
?T 0.5 0.8 deg
(at the target)
f
f
April 05 _at_ iThemba labs.
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Horizontal plane (X-plane) correction
for a better energy resolution
T Horizontal scattering angle deg
X The horizontal position mm
X The horizontal position mm
Before calibrations
Curving and broadened
April 05 _at_ iThemba labs.
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X-THETA correction
Small region is projected to X-axis.
Gaussian fitting
Another region is selected and projected.
Projected to X-axis
Gaussian fitting
The curving shapes are represented numerically.
April 05 _at_ iThemba labs.
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The progress of the energy resolution
Ex 11.45MeV 1
20keV
April 05 _at_ iThemba labs.
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Background subtraction (I)
True events
rotated
projection
Backgraound
f
Y The vertical position mm
This rotation corresponds to move the VDC to the
Y focal plane.
April 05 _at_ iThemba labs.
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Background subtraction (II)
Uniform BKG
April 05 _at_ iThemba labs.
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A high quality spectrum
preliminary
April 05 _at_ iThemba labs.
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G.M. Crawley et al, PRC39(1989)311, at Orsay
2000
1500
500
Present data
preliminary
April 05 _at_ iThemba labs.
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The Differential Cross Section
OXBASH parameter from A. Willis et al., PRC
43(1991)5
preliminary
April 05 _at_ iThemba labs.
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Strength distributions
Ep 200 MeV
M1 states only
B(s) (µn2)
All strengths are normalized by the data of
Crawley at 11.45 MeV.
Ep 160 MeV
preliminary
M1 unknown states
B(s) (µn2)
Ep 295 MeV
M1 unknown states
preliminary
Excitation Energy (MeV)
April 05 _at_ iThemba labs.
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E249 data
These spectra were obtained in the E249
experiment.
targets 02.54.5 28Si ? ?
? 1.9 mg/cm2 (natural) 48Ca ? ? ? 1.9 mg/cm2
64Ni ? ? ? 4.7 mg/cm2 12C ? ? ? 1.1 mg/cm2
Mylar ? ? ? 1.0 mg/cm2 13CH2 ? - - 0.7
mg/cm2 24Mg ? - - 1.8 mg/cm2 26Mg ? -
- 1.6 mg/cm2 40Ca ? - - 13 mg/cm2 90Zr ?
- - 1.0 mg/cm2 ?... measured, ?...
good statistics, ?... poor statistics, -...
not measured
April 05 _at_ iThemba labs.
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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 0.50.8
  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 _at_ iThemba labs.
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Future

• Jp assignments of each peak
• Extraction of M1 strengths and their
  distributions
• Next beam time
• At finite angles
• Data for further calibrations

April 05 _at_ iThemba labs.