# Shell evolution approaching the N=20 island of inversion: Structure of 29Mg

## TL;DR

This study investigates the structure of 29Mg near the N=20 island of inversion, combining experimental measurements of single-particle states with advanced shell model calculations to understand shell evolution in neutron-rich nuclei.

## Contribution

It provides the first quantitative measurements of 29Mg's single-particle structure and compares these with state-of-the-art shell model predictions, highlighting areas of agreement and discrepancy.

## Key findings

- Two key states with significant f-wave strength identified at 2.40 and 4.28 MeV.
- Shell model describes the lowest 7/2- levels well.
- Discrepancies in the sharing of single-particle strength for 3/2- and 5/2- levels.

## Abstract

The "Island of Inversion" for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modelling of shell evolution with isospin. In this context, the structure of the transitional nucleus 29Mg is critical. The first quantitative measurements of the single particle structure of 29Mg are reported, using data from the d(28Mg,p gamma)29Mg reaction. Two key states carrying significant ell=3 (f-wave) strength were identified at 2.40 +/- 0.10 (Jpi = 5/2-) and 4.28 +/- 0.04 MeV (7/2-). New state-of-the-art shell model calculations have been performed and the predictions are compared in detail with the experimental results. Whilst the two lowest 7/2- levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2- and 5/2- levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell model calculations.