Nature of yrast excitations near N=40: Level structure of Ni-67

TL;DR

This study investigates the level structure of Ni-67 near N=40, revealing complex configurations and the weak N=40 subshell gap through experimental data and shell model calculations.

Contribution

It provides a detailed level scheme of Ni-67 up to 5.3 MeV and demonstrates the significance of multi particle-hole excitations involving the g9/2 neutron orbital.

Findings

Yrast states are linked to complex configurations.

Weak N=40 subshell gap evidenced by multi particle-hole excitations.

Agreement between experimental data and shell model calculations.

Abstract

Excited states in Ni-67 were populated in deep-inelastic reactions of a Ni-64 beam at 430 MeV on a thick U-238 target. A level scheme built on the previously known 13 micro-s isomer has been delineated up to an excitation energy of ~5.3 MeV and a tentative spin and parity of (21/2-). Shell model calculations have been carried out using two effective interactions in the f5/2pg9/2 model space with a Ni-56 core. Satisfactory agreement between experiment and theory is achieved for the measured transition energies and branching ratios. The calculations indicate that the yrast states are associated with rather complex configurations, herewith demonstrating the relative weakness of the N=40 subshell gap and the importance of multi particle-hole excitations involving the g9/2 neutron orbital.