Transcript RISING Spectroscopy at relativistic energies

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IUAC
Lifetime measurement of 2+ excitation
in nuclei far away from stability
H.J. Wollersheim, P. Doornenbal, J. Gerl
Gesellschaft für Schwerionenforschung, P.O. Box 110552, D-64291
Darmstadt, Germany
A. Dewald, K.O. Zell
Institut für Kernphysik, Universität Köln, Zülpicherstrasse 77, D50937 Köln, Germany
R.K. Bhowmik, R. Kumar, S. Muralithar, R.P. Singh
Inter University Accelerator Centre, New Delhi 110067, India
S.K. Mandal, Ranjeet
Department of Physics & Astrophysics, University of Delhi, New
Delhi 110007, India
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New Shell Structure at N>>Z
Experiments with N=28-34 Nuclei
Neutron-rich Ca-, Ti-, Cr-Isotopes
• few protons in pf7/2 shell
• weaker pf7/2 –nf5/2 monopole
pairing interactions
• nf5/2 moves up in energy
• possible shell gaps at N=32
and N=34?
56Ti
22
Vst
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New Shell Structure at N>>Z
Experiments with N=28-34 Nuclei
Comparison: 2+ systematics
and shell model calculations
• N=32 for Z24 (Cr)
• N=32, N=34 for Z  22 (Ti)
Transition matrix elements?
Theory:GXPF1, GXPF1A
M.Honma et al, Phys. Rev. C65(2002)061301
KB3G
E.Caurier et al, Eur.Phys.J. A 15, 145 (2002)
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Comparison with large-scale shell-model calculation
• Experimental 2+ energy high
for 56Cr32
• Experimental B(E2) value
lower for 56Cr32 than for 54Cr
and 58Cr
• Theory does not reproduce the
56Cr B(E2) value
•
New Shell closure at N = 34 ??
Calculations:
T. Otsuka et al., Phys. Rev. Lett. 87, 082502 (2001)
T. Otsuka et al., Eur. Phys. J. A 13,69 (2002)
M. Honma et al., Phys. Rev. C 69, 034335 (2004)
E. Caurier et al., Eur. Phys. J. A 15, 145 (2002)
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Systematic Errors in Coulomb Excitation
• Angle measurement
• Nuclear correction
RIKEN 50 MeV/A
MSU
40 MeV/A
GANIL 30 MeV/A
CERN
2 MeV/A
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Rare ISotope INvestigation at GSI
Spectroscopy at relativistic energies
Fragment Separator FRS provides secondary RIB
• fragmentation and fission of primary beams
• high secondary beam energies: 100 – 500 MeV/u
• fully stripped ions
FRS
RISING
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Tracking: scattering angle determination
MW MW
Target
 Doppler corr. of measured g-rays
 impact parameter measurement
Qp
Qg
g
Exp. difficulty:
angular straggling ~8mrad
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 How to distinguish nuclear excitation ?
 How to separate nuclear absorption ?
Solution:
Relative measurement of B(E2)-values
for different isotopes
dσ/dθp [arb.]
 Coulomb excitation <θmax
CATE
Si CsI
Limit in scattering
angles 0.6o to 2.8o
corresponds to
impact parameters:
40 to 10 fm
scattering angle θp [deg]
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MSU experiment:
Neutron-rich Ti isotopes and N=32 and N=34 shell gaps
Coulomb + nuclear excitation
(model dependent)
new lifetime measurement
for 52Ti needed
D.-C.Dinca et al. Phys. Rev. C71 (2005) 041302
B.A. Brown et al. Phys. Rev. C14 (1976) 1016
Eg
[keV]
B(E2;0+→2+)
[e2fm4]
52Ti
1050
567(51)
54Ti
1497
357(63)
56Ti
1123
599(197)
Prev. work
[e2fm4]
665
 515
 415
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Direct measurement of B(E2) for 52Ti
B.A. Brown et al. Phys. Rev. C14 (1976) 1016
7Li
+ 48Ca at 28 MeV populated
51Ti, 52Ti, 52V
Lifetime measurements by RDM technique (singles)
• 1050 keV state a doublet !
• Large uncertainties in
extraction of B(E2) of 52Ti
(2+ 0+) transition
t20 ~ 4.8 ( +8.0 -2.1) ps
• 710 keV line contaminated
by 72Ge(n,n') at 692 keV
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EXPERIMENT DONE AT NSC
• Experiment with RDM facility at GDA setup
• 7Li beam at 28 MeV
• 48Ca on stretched Au foil provided by GSI
• Measurements done in gg coincidence mode
to eliminate contaminant transitions & sidefeeding
• Differential Decay Curve Method (DDCM)
for life time extraction
Problems faced
• 6+ 4+ transition has long half-life ( ~ 35 ps)
• Initial feeding of 2+ state sensitive to lifetime
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Lifetime Measurements on 52Ti
48Ca
targets supplied
by GSI
RDM experiments
with 7Li beam at
IUAC
gg spectra collected
at different stopper
distances
Oxidation of 48Ca
target in transit
prevented
measurements below
20 mm distance
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Lifetime Measurements on 52Ti
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Lifetime Measurements on 52Ti
Present Results:
Lifetime of
6+ state in 52Ti = 67.5 +6.9 -4.9 ps
9+ state in 52V = 6.62 +0.39 -0.31 ps
Initial feeding of 2+ state in 52Ti could not be measured at
the minimum distance of approach ( ~ 20 mm) limited by
target wrinkles due to oxidation in transit
It will be useful to do a differential curve analysis
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BE(2) values in light Sn isotopes
• Stable Sn isotopes fall in
between magic shells at
N=50 & 82
• B(E2) for Sn isotopes
maximum at mid-shell
• Large error bars for
isotopes lighter than 116Sn
• Measurements on 108Sn
done earlier at GSI by
Coulomb excitation
• Accurate relative B(E2) for
112,114Sn / 116Sn required
Sn-isotopes
RIB
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•
Coulomb Excitation at GSI
114, 116Sn
beams of 3.6
MeV/A on 58Ni target.
• Coulomb excitation of
projectile and target
• Two super-clovers used
with electronics developed
at IUAC
• Participation by Rakesh
Kumar, R.P. Singh and A.
Jhinghan from IUAC
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Coulomb Excitation of Sn isotopes
Doppler Corrected Spectra 
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Angular
Distribution for Coulomb Excitation
qlab = 15- 45
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EXPERIMENT PLANNED AT IUAC
 190 MeV 58Ni beam on 112Sn target (1% abundance)
 Target to be enriched to >99.5% purity
 Measurement of Coulomb excitation for 58Ni & 112Sn with
g-rays to be detected in coincidence with scattered
beam/recoils in annular position-sensitive PPAC developed
at IUAC
 qlab = 15 - 45
 qcm = 23 - 67 for 58Ni & 90 - 150 for 112Sn
 Cross-sections of ~ 120 mb expected for both projectile &
target excitation
 g to be detected by 4 Clover detectors at 153
 Peak counts ~ 104 expected in 3 days of beam time
 Total beam time requested 5 days including setup time
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