Large scale shell model calculations along Z=28 and N=50 closures: towards the doubly-magic 78Ni

TL;DR

This paper uses advanced shell model calculations to study the structure of nuclei near 78Ni, revealing the robustness of the N=50 shell gap and its evolution across isotopic chains, which informs understanding of nuclear shell closures.

Contribution

The study performs large-scale shell model calculations across Z=28 and N=50 shells, providing new insights into shell gap evolution and cross-shell excitations near 78Ni.

Findings

Confirmed the robustness of the N=50 shell gap in 78Ni.

Identified the minimum of the N=50 gap at Z=32.

Compared the N=50 gap evolution with oxygen and calcium chains.

Abstract

We present the state-of-the art shell model calculations in a large model space (pf for protons, fpgd for neutrons), which allow to study simultaneously excitations across the Z=28 and N=50 shell gaps. We explore the region in the vicinity of 78Ni, being a subject of intense experimental investigations. Our calculations account correctly for the known low lying excited states in this region, including those which may correspond to cross-shell excitations. We observe the minimum of the N=50 mass gap at Z=32 consistent with experimental data and its further increase towards Z=28, indicating a robustness of the N=50 gap in 78Ni. The evolution of N=50 gap along the nickel chain is shown to bear similarities with what is know in oxygen and calcium chains, providing a new opportunity for the studies of 3-body monopole effects in medium mass nuclei.