Coulomb-excitation of the exotic, neutron-rich nuclei 94Kr and 96Kr

Nuclei in the neutron-rich A∝100 mass region are well suited for the understanding of the development of collectivity. By adding only a few neutrons to the N=50 shell closure, collective effects can quickly occur. For the Z=40 (Zr) isotopes, N=56 becomes an effective shell closure, so that 96Zr is quoted as a doubly-magic nucleus. Adding only a few neutrons more, the Zr-isotopes get strongly deformed. This behavior indicates a shape phase transition at N=60 from spherical to deformed shapes. For the Z=38 (Sr) and Z=42 (Mo) isotopes the systematics show a similar behavior, whereas for the Z=44 (Ru) isotopes, this rapid change of shape seems to be attenuated. The aim of our work was to investigate the behavior of the Z=36 (Kr) isotopes in this phase transition region by determining the energies of the 2+1 states and their E2 decay transition strengths to the ground state in 94Kr (N=58) and 96Kr (N=60). Therefore, we performed two experiments at REX-ISOLDE at CERN, utilizing the high-efficiency MINIBALL γ-ray spectrometer and analyzing the emitted γ-rays and scattered particles after the Coulomb-excitation reactions 196Pt(94Kr, 94Kr*)196Pt* and 196Pt(96Kr, 96Kr*)196Pt*. We show and discuss the preliminary results.