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

The lifetime of the 0(3)(+) state in Ni-66, two neutrons below the N = 40 subshell gap, has been measured. The transition B(E2; 0(3)(+) -> 2(1)(+)) is one of the most hindered E2 transitions in the Ni isotopic chain and it implies that, unlike Ni-68, 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; 0(3)(+)-> 2(1)(+)) value.