Evolution of shell structure in exotic nuclei

TL;DR

This paper reviews how the shell structure of atomic nuclei evolves in exotic, unstable isotopes, highlighting the interplay of nuclear forces and experimental evidence for changing magic numbers.

Contribution

It provides a comprehensive overview of the theoretical mechanisms driving shell evolution and links them to experimental observations in exotic nuclei.

Findings

Shell closures change in exotic nuclei compared to stable ones.

Nuclear forces' components significantly influence shell evolution.

Experimental data reveal new magic numbers in unstable isotopes.

Abstract

The atomic nucleus is a quantum many-body system whose constituent nucleons (protons and neutrons) are subject to complex nucleon-nucleon interactions that include spin- and isospin-dependent components. For stable nuclei, already several decades ago, emerging seemingly regular patterns in some observables could be described successfully within a shell-model picture that results in particularly stable nuclei at certain magic fillings of the shells with protons and/or neutrons: N,Z = 8, 20, 28, 50, 82, 126. However, in short-lived, so-called exotic nuclei or rare isotopes, characterized by a large N/Z asymmetry and located far away from the valley of beta stability on the nuclear chart, these magic numbers, viewed through observables, were shown to change. These changes in the regime of exotic nuclei offer an unprecedented view at the roles of the various components of the nuclear force when theoretical descriptions are confronted with experimental data on exotic nuclei where certain effects are enhanced. This article reviews the driving forces behind shell evolution from a theoretical point of view and connects this to experimental signatures.