Level densities of nickel isotopes: microscopic theory versus experiment

TL;DR

This study uses advanced microscopic methods to accurately calculate the level densities of nickel isotopes, showing excellent agreement with experimental data and providing insights into nuclear structure at various excitation energies.

Contribution

The paper introduces a spin-projection shell model Monte Carlo approach combined with Green's function techniques to compute nickel isotope level densities microscopically.

Findings

Excellent agreement with proton evaporation spectra data

Good match with level counting data at low energies

Discrepancy observed in $^{63}$Ni neutron resonance data

Abstract

We apply a spin-projection method to calculate microscopically the level densities of a family of nickel isotopes $^{59-64}$Ni using the shell model Monte Carlo approach in the complete $pfg_{9/2}$ shell. Accurate ground-state energies of the odd-mass nickel isotopes, required for the determination of excitation energies, are determined using the Green's function method recently introduced to circumvent the odd particle-number sign problem. Our results are in excellent agreement with recent measurements based on proton evaporation spectra and with level counting data at low excitation energies. We also compare our results with neutron resonance data, assuming equilibration of parity and a spin-cutoff model for the spin distribution at the neutron binding energy, and find good agreement with the exception of $^{63}$Ni.