Lifetime measurement of 2 + excitation in nuclei far away from stability

1. Lifetime measurement of 2+ excitation in nuclei far away from stability IUAC 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, D-50937 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

2. New Shell Structure at N>>Z Experiments with N=28-34 Nuclei • Neutron-rich Ca-, Ti-, Cr-Isotopes • fewprotons 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? Vst 56Ti22

3. 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)

4. 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)

5. 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

6. 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

7. Tracking: scattering angle determination MW MW Target CATE Si CsI Qp Qg g • Doppler corr. of measured g-rays  impact parameter measurement Exp. difficulty: angular straggling ~8mrad • Coulomb excitation <θmax • How to distinguish nuclear excitation ? • How to separate nuclear absorption ? Solution: Relative measurement of B(E2)-values for different isotopes 200 Limit in scattering angles 0.6o to 2.8o corresponds to impact parameters: 40 to 10 fm dσ/dθp [arb.] scattering angle θp [deg]

8. 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

9. 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

10. EXPERIMENT DONE AT NSC Experiment withRDM 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 & side-feeding 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

11. 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

12. Lifetime Measurements on 52Ti

13. 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

14. 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

15. 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

16. Coulomb Excitation of Sn isotopes Doppler Corrected Spectra 

17. Angular Distribution for Coulomb Excitation qlab = 15- 45

18. EXPERIMENT PLANNED AT IUAC 190 MeV 58Ni beam on112Sn 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