Shell evolution and E-2 collectivity: new spectroscopic information

We report here on the first evidence for shape coexistence caused by Type II Shell Evolution which is firmly based on the measurement of absolute E2 transition rates. The data have been obtained in high-resolution inelastic electron scattering spectroscopy of the nucleus Zr-96 at the Superconducting Darmstadt Linear electron Accelerator (S-DALINAC). The data are presented and discussed. The neutron sub-shell closure at neutron number N = 56 plays a crucial role for the occurence of shape coexistence in Zr-96,Zr-98. We have studied the structure of exotic neutron-rich isotopes near the N = 56 neutron sub-shell closure using gamma-ray spectroscopy and radioactive beams. We also present and discuss spectroscopic data on Ge-84,Ge-86,Ge-88 taken recently at RIBF, RIKEN. The new data suggest the hitherto unknown existence of a region of pronounced nuclear triaxiality in neutron-rich Ge isotopes.