Detailed low-spin spectroscopy of Ni65 via neutron capture reaction

An extended investigation of the low-spin structure of the $^{65}\mathrm{Ni}$ nucleus was performed at the Institut Laue-Langevin, Grenoble, France, via the neutron capture reaction $^{64}\mathrm{Ni}(n,\ensuremath{\gamma})^{65}\mathrm{Ni}$, using the Fission Product Prompt Gamma-Ray Spectrometer High-Purity Ge array. The level scheme of $^{65}\mathrm{Ni}$ was significantly expanded, with two new levels and 87 newly found transitions. Angular correlation analyses were also performed, allowing us to assign spins and parities for a number of states and to determine multipolarity mixing ratios for selected $\ensuremath{\gamma}$ transitions. The low-energy part of the experimental level scheme (up to about 1.4 MeV) was compared with Monte Carlo shell-model calculations, which predict spherical shapes for all states, apart from the $9/{2}^{+}$ and the second excited $1/{2}^{\ensuremath{-}}$ states of oblate deformation.