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 The Z~20, N~34region It is known experimentally that the neutron νf5/2 orbit from 57Ni towards 49Ca undergoes a large monopole shift due to the reduced binding with increasing removal of the proton f7/2 S=0 spin-orbit partners. Beyond N=28 this opens a gap between the ν(p3/2,p1/2) and νf5/2 orbits, which might be subject to change depending on the 2p1/2 position, as this also forms a S=0 pair with π1f7/2 but with less radial overlap. In the figure experimental signatures for shell structure are shown: the two-nucleon separation energy differences δ2n/δ2p, the 2+ excitation energies E(2+), the B(E2;2+ →0+) values In the Ca isotopes beyond N=28 a possible (sub)shell closure at N=32,34 seems to develop in E(2+). The Cr isotopes show a maximum in E(2+) at N=32. On the other hand within the N=34 isotones E(2+) is increasing from Fe to Cr in contrast to the expected trend towards midshell, which supports a N=34 closure. Besides masses, which due to short half lives are difficult to measure, obviously E(2+) and B(E2) values for 50-54Ca are missing for a proof of the concept. Similarly a study of the N=30-34 isotones of Cr and Ti would reveal such a change in shell structure. The shell behaviour in the N~40-50 region is dominated by the monopole strength of the πf5/2 νg9/2 and πf7/2 νf5/2 pairs of nucleons, which is known from experiment. At N=40 68Ni as an isolated nucleus exhibits doubly-magic features, which rapidly disappear when adding protons into πf5/2 or removing them from πf7/2 as in both cases the gap between νg9/2 and νf5/2 is closed by increased νg9/2 and decreased νf5/2 binding, respectively. It is an interesting question whether this affects the N=50 shell at 78Ni, too, where the πf5/2 orbit is empty, which shifts νg9/2 towards νd5/2.

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? Vst 56Ti22 The Z~20, N~34region It is known experimentally that the neutron νf5/2 orbit from 57Ni towards 49Ca undergoes a large monopole shift due to the reduced binding with increasing removal of the proton f7/2 S=0 spin-orbit partners. Beyond N=28 this opens a gap between the ν(p3/2,p1/2) and νf5/2 orbits, which might be subject to change depending on the 2p1/2 position, as this also forms a S=0 pair with π1f7/2 but with less radial overlap. In the figure experimental signatures for shell structure are shown: the two-nucleon separation energy differences δ2n/δ2p, the 2+ excitation energies E(2+), the B(E2;2+ →0+) values In the Ca isotopes beyond N=28 a possible (sub)shell closure at N=32,34 seems to develop in E(2+). The Cr isotopes show a maximum in E(2+) at N=32. On the other hand within the N=34 isotones E(2+) is increasing from Fe to Cr in contrast to the expected trend towards midshell, which supports a N=34 closure. Besides masses, which due to short half lives are difficult to measure, obviously E(2+) and B(E2) values for 50-54Ca are missing for a proof of the concept. Similarly a study of the N=30-34 isotones of Cr and Ti would reveal such a change in shell structure. The shell behaviour in the N~40-50 region is dominated by the monopole strength of the πf5/2 νg9/2 and πf7/2 νf5/2 pairs of nucleons, which is known from experiment. At N=40 68Ni as an isolated nucleus exhibits doubly-magic features, which rapidly disappear when adding protons into πf5/2 or removing them from πf7/2 as in both cases the gap between νg9/2 and νf5/2 is closed by increased νg9/2 and decreased νf5/2 binding, respectively. It is an interesting question whether this affects the N=50 shell at 78Ni, too, where the πf5/2 orbit is empty, which shifts νg9/2 towards νd5/2.

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? The Z~20, N~34region It is known experimentally that the neutron νf5/2 orbit from 57Ni towards 49Ca undergoes a large monopole shift due to the reduced binding with increasing removal of the proton f7/2 S=0 spin-orbit partners. Beyond N=28 this opens a gap between the ν(p3/2,p1/2) and νf5/2 orbits, which might be subject to change depending on the 2p1/2 position, as this also forms a S=0 pair with π1f7/2 but with less radial overlap. In the figure experimental signatures for shell structure are shown: the two-nucleon separation energy differences δ2n/δ2p, the 2+ excitation energies E(2+), the B(E2;2+ →0+) values In the Ca isotopes beyond N=28 a possible (sub)shell closure at N=32,34 seems to develop in E(2+). The Cr isotopes show a maximum in E(2+) at N=32. On the other hand within the N=34 isotones E(2+) is increasing from Fe to Cr in contrast to the expected trend towards midshell, which supports a N=34 closure. Besides masses, which due to short half lives are difficult to measure, obviously E(2+) and B(E2) values for 50-54Ca are missing for a proof of the concept. Similarly a study of the N=30-34 isotones of Cr and Ti would reveal such a change in shell structure. The shell behaviour in the N~40-50 region is dominated by the monopole strength of the πf5/2 νg9/2 and πf7/2 νf5/2 pairs of nucleons, which is known from experiment. At N=40 68Ni as an isolated nucleus exhibits doubly-magic features, which rapidly disappear when adding protons into πf5/2 or removing them from πf7/2 as in both cases the gap between νg9/2 and νf5/2 is closed by increased νg9/2 and decreased νf5/2 binding, respectively. It is an interesting question whether this affects the N=50 shell at 78Ni, too, where the πf5/2 orbit is empty, which shifts νg9/2 towards νd5/2. Theory:GXPF1, GXPF1A M.Honma et al, Phys. Rev. C65(2002)061301 KB3G E.Caurier et al, Eur.Phys.J. A 15, 145 (2002)

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)

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

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

Tracking: scattering angle determination 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 Qp g Qg MW CATE Si CsI Target 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]

MSU experiment: Neutron-rich Ti isotopes and N=32 and N=34 shell gaps Eg [keV] B(E2;0+→2+) [e2fm4] Prev. work [e2fm4] 52Ti 1050 567(51) 54Ti 1497 357(63) --- 56Ti 1123 599(197) 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

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

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 & 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

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

Lifetime Measurements on 52Ti

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

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

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

Coulomb Excitation of Sn isotopes Doppler Corrected Spectra 

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

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