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.