Experimental $\gamma$-decay strength in $^{59, 60}$Ni compared with microscopic calculations

TL;DR

This study measures gamma-decay strength functions in nickel isotopes using experimental methods and compares them with microscopic theoretical calculations, revealing insights into nuclear structure and decay processes.

Contribution

It provides new experimental gamma-decay strength data for $^{59,60}$Ni and compares these with shell model and QTBA calculations, enhancing understanding of nuclear decay mechanisms.

Findings

Gamma-ray strength functions increase at low energies.

Shell model calculations qualitatively match low-energy data.

QTBA describes data above 7 MeV.

Abstract

Nuclear level densities and $\gamma$-ray strength functions have been extracted for $^{59, 60}\rm{Ni}$, using the Oslo method on data sets from the $^{60}$Ni($^{3}$He,$^{3}$He$^{\prime}\gamma$)$^{60}$Ni and $^{60}$Ni($^{3}$He,$\alpha\gamma$)$^{59}$Ni reactions. Above the neutron separation energy, S$_n$, we have measured the $\gamma$-ray strength functions for $^{61}$Ni and $^{60}$Ni in photoneutron experiments. The low-energy part of the $^{59,60}$Ni $\gamma$-ray strength functions show an increase for decreasing $\gamma$ energies. The experimental $\gamma$-ray strength functions are compared with $M1$ $\gamma$-ray strength functions calculated within the shell model. The $E1$ $\gamma$-ray strength function of $^{60}$Ni has been calculated using the QTBA framework. The QTBA calculations describe the data above $E_{\gamma}\approx$ 7 MeV, while the shell-model calculations agree qualitatively with the low energy part of the $\gamma$-ray strength function. Hence, we give a plausible explanation of the observed shape of the $\gamma$-decay strength.