Abstract

Abstract The νg$_9/2$, d$_5/2$, s$_1/2$ orbitals are assumed to be responsible for the swift onset of collectivity observed in the region below $^68$Ni. Especially the single-particle energies and strengths of these orbitals are of importance. We studied such properties in the nearby $^67$Ni nucleus, by performing a (d,p)-experiment in inverse kinematics employing a post-accelerated radioactive ion beam (RIB) at the REX-ISOLDE facility. The experiment was performed at an energy of 2.95 MeV/u using a combination of the T-REX particle detectors, the Miniball γ-detection array and a newly-developed delayed-correlation technique as to investigate μs-isomers. Angular distributions of the ground state and multiple excited states in $^67$Ni were obtained and compared with DWBA cross-section calculations, leading to the identification of positive-parity states with substantial νg$_9/2$ (1007 keV) and νd$_5/2$ (2207 keV and 3277 keV) single-particle strengths up to an excitation energy of 5.8 MeV. 50\% of the νd$_5/2$ single-particle strength relative to the νg$_9/2-orbital is concentrated in and shared between the first two observed 5/2^+ levels. A comparison with extended Shell Model calculations and equivalent ($^3$He, d) studies in the region around $^90_40$Zr$_50$ highlights similarities for the strength of the negative-parity pf and positive-parity g$_9/2$ state, but differences are observed for the d$_5/2 single-particle strength.

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