New Shell Structure at N>>Z Lifetime measurement of the first excited 2+ state in 52Ti 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 Nuclear Science Centre, P.O. Box 10502, 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 Collaboration: Cologne, GSI, NSC, Delhi Spokesperson: H.J. Wollersheim, R.K. Bhowmik f 5/2 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. Neutron-rich Ca-, Ti-, Cr-Isotopes protons are removed from the 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?

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)

Rare ISotope INvestigation at GSI Spectroscopy at relativistic energies Fragment Separator FRS provides secondary radioactive ion beams: fragmentation and fission of primary beams high secondary beam energies: 100 – 500 MeV/u fully stripped ions FRS RISING

RISING experimental setup Ge Cluster detectors Target chamber CATE beam BaF2 HECTOR detectors

New Shell Structure at N>>Z Relativistic Coulex in N=28-34 Nuclei B(E2) values for 56,58Cr Eg [keV] Nions Ig eff.corr.. This work B(E2) [Wu] Prev. work B(E2) [Wu] 54Cr 835 3.0·107 21300 Normali- sation 14.6(6) 56Cr 1006 1.5·107 6500 8.5 (2.5) --- 58Cr 880 1.0·107 7800 14.1 (3.9) PRELIMINARY RISING results from A. Bürger, Bonn

Tracking: scattering angle determination Doppler correction 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 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 possible 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

Relativistic Coulomb Excitation of Nuclei Near 100Sn Collaboration: Lund, Uppsala, Stockholm, Keele, Legnaro, Warsaw, Debrecen, Liverpool, Surrey, York, GSI Spokesperson: C. Fahlander, Lund, M. Gorska, GSI ORNL data RISING B(E2, 2+->0+) values provide E2 correlations related to core polarization. Lifetime measurements hampered by low-lying isomeric 6+ states in even Sn isotopes up to 102Sn 2+->0+ decay too fast for electronic timing methods. Coulomb excitation of instable Sn isotopes

Relativistic Coulomb Excitation of Nuclei Near 100Sn Primary beam: 124Xe: 700 MeV/u Secondary beam: 112Sn: 147 MeV/u, 3500 1/s, 35 hours 108Sn: 142 MeV/u, 3500 1/s, 24 hours Coulomb excitation: Au-target: 400 mg/cm2 Limited statistics due to VXI failure (2/3 of uncorrelated data, low efficiency with five Clusters at outer detector rings) Preliminary B(E2, 2+->0+) value: 108Sn: 10.3 +/- 2.0 W.u. Theory: 108Sn: 11.49 W.u. M. Hjorthen-Jensen, priv. com. 108Sn: 10.54 W.u. E. Caurier, F. Nowacki, priv. com. 112Sn (2+  0+) 108Sn (2+  0+) results from A. Banu, M. Gorska, GSI