High-precision spectroscopy of Ni-65 via neutron capture

Detailed studies of the low-spin structures of neutron-rich Ni isotopes may help shedding light on the shape coexistence phenomenon. Of particular interest is the Ni-65 nucleus, since it lies between Ni-64 and Ni-66, where shape coexistence has been reported earlier. A spectroscopic investigation of Ni-65 has been performed at Institut Laue-Langevin via the reaction Ni-64(n, gamma) Ni-65, using the FIPPS HPGe array. Several new gamma transitions have been observed and angular correlation analyses have been performed. A comparison with Monte Carlo shell-model calculations pointed to a dominance of spherical states up to 1.5 MeV excitation energy, together with the appearance of two states of oblate character.