First Indication for Shape Transitions in Neutron-rich Selenium Isotopes

Neutron-rich 88,90,92,94Se isotopes were studied via in-beam γ-ray spectroscopy after production from nucleon removal at intermediate energies at the Radioactive Isotope Beam Factory. γ-γ coincidence analysis allowed to establish level schemes for the first time in these nuclei, including the 2+ 1 → 0 + gs, 4+ 1 → 2 + 1 transitions and their energy ratio R4/2. Low-lying 2+ 2 levels and their branching to the 2+ 1 and 0+ gs states were observed. The experimental results are in good agreement with self-consistent beyond-mean-field calculations based on the Gogny D1S interaction, suggesting ground state shape transition from oblate to prolate then back to oblate between N = 52 − 60 and indicating shape coexistence