Catching shape isomerism in Ni nuclei with experiment and theory

In an experiment performed at the Tandem Accelerator Laboratory in Bucharest, a shape-isomer-like structure at spin zero in a very light nucleus, ⁶⁶Ni, has been identified, by using gamma-ray spectroscopy and employing the two-neutron transfer reaction induced by an ¹⁸O beam on a ⁶⁴Ni target, at sub-Coulomb barrier energy. The study was inspired by various mean-field theoretical approaches as well as by the state-of-the-art Monte Carlo Shell Model Calculations, all pointing to ⁶⁶Ni as the lightest nucleus with a pronounced secondary prolate minimum in the nuclear potential energy surface, at spin zero. New experimental campaigns are on going in Bucharest, ILL (Grenoble) and IPN-Orsay, in order to pin down, in great details, the origin of the shape coexistence phenomenon in neutron-rich Ni isotopes, possibly locating other examples of shape isomerism in this region. Preliminary results are shown on ⁶⁴Ni, in comparison with MCSM predictions. This extended investigation is expected to shed light on the microscopic origin of nuclear deformation along the Ni isotopic chain. (author)