Search for shape-coexisting 0+ states in Ni 66 from lifetime measurements

The lifetime of the 03+ state in Ni66, two neutrons below the N=40 subshell gap, has been measured. The transition B(E2;03+→21+) is one of the most hindered E2 transitions in the Ni isotopic chain and it implies that, unlike Ni68, there is a spherical structure at low excitation energy. We have performed extensive shell-model calculations that correctly predict this result, obtaining a spherical 0+ state at the correct energy and with an extremely low B(E2;03+→21+) value.