Seniority and $(\frac{9}{2})^n$ configurations in neutron-rich Nickel isotopes

TL;DR

This paper investigates the excited states of neutron-rich Nickel isotopes using pairing interactions and seniority models to understand their energy spectra and state ordering.

Contribution

It introduces a combined approach of pairing forces and seniority models to predict and analyze energy levels in Nickel isotopes, including state ordering and multiplet structures.

Findings

Successful reproduction of ground state multiplets with seniority ν=2.

Predictions of ν=3 and ν=4 states in odd-even and even-even isotopes.

Comparison with N=50 isotones shows structural similarities.

Abstract

Excited states in low-energy spectra in $^{70-76}$Ni are considered. To this end, pairing forces in form of surface delta interaction are employed to account for formation of the ground state multiplet with seniority $\nu = 2$ states. The multiplet splitting is described with mass relations of masses of neighbouring nuclei. Subsequently, seniority model is used to reproduce or predict the states $\nu = 3$ in odd-even isotopes and $\nu = 4$ in even-even isotopes. Correct account of $2_1^+$ state should allow for description of reversed order of states $J = 4$ with $\nu = 2$ and $\nu = 4$ observed in experiment. The results obtained are compared with the structure of similar multiplets in $N=50$ isotones.