Shell evolution and E2 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 ⁹⁶Zr 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 ⁹⁶,⁹⁸Zr. We have studied the structure of exotic neutron-rich isotopes near the N = 56 neutron sub-shell closure using γ-ray spectroscopy and radioactive beams. We also present and discuss spectroscopic data on ⁸⁴,⁸⁶,⁸⁸Ge 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.