Evolution of the N=28 shell closure: a test bench for nuclear forces

TL;DR

This paper investigates how the N=28 shell closure evolves far from stability, comparing experimental data with theoretical models to understand the effects of various nuclear force components on shell gaps and spin-orbit splittings.

Contribution

It provides a comprehensive analysis of the N=28 shell closure evolution, highlighting the roles of different nucleon-nucleon interaction terms and proposing analogies with other magic numbers.

Findings

Identification of the effects of central, spin-orbit, tensor, and three-body forces on shell gap modifications.

Comparison of experimental results with theoretical predictions to understand shell evolution.

Discussion of implications for drip-line nuclei, bubble nuclei, and r-process nucleosynthesis.

Abstract

The evolution of the N=28 shell closure is investigated far from stability. Using the latest results obtained from various experimental techniques, we discuss the main properties of the N=28 isotones, as well as those of the N=27 and N=29 isotones. Experimental results are confronted to various theoretical predictions. These studies pinpoint the effects of several terms of the nucleon-nucleon interaction, such as the central, the spin-orbit, the tensor and the three-body force components, to account for the modification of the N=28 shell gap and spin-orbit splittings. Analogies between the evolution of the N=28 shell closure and other magic numbers originating from the spin-orbit interaction are proposed (N=14,50, 82 and 90). More generally, questions related to the evolution of nuclear forces towards the drip-line, in bubble nuclei, and for nuclei involved in the r-process nucleosynthesis are proposed and discussed.