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

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.

Comments: to be published in Chinese Physics C