Border of the Island of Inversion: Unbound states in $^{29}$Ne

TL;DR

This study investigates unbound states of $^{29}$Ne near the island of inversion, providing the first evidence of $f_{7/2}$ single particle strength through resonance analysis and shell-model comparisons.

Contribution

It reports the first observation of unbound states in $^{29}$Ne and identifies $f_{7/2}$ single particle strength, advancing understanding of nuclear structure at the island of inversion boundary.

Findings

First evidence of $f_{7/2}$ strength in $^{29}$Ne

Observation of a resonance at 1.48 MeV with $ ext{l}$=3 component

Comparison with shell-model calculations confirms state properties

Abstract

The nucleus $^{29}$Ne is situated at the border of the island of inversion. Despite significant efforts, no bound low-lying intruder $f_{7/2}$-state, which would place $^{29}$Ne firmly inside the island of inversion, has yet been observed. Here, the first investigation of unbound states of $^{29}$Ne is reported. The states were populated in $^{30}\mathrm{Ne}(p,pn)$ and $^{30}\mathrm{Na}(p,2p)$ reactions at a beam energy of around $230$ MeV/nucleon, and analyzed in terms of their resonance properties, partial cross sections and momentum distributions. The momentum distributions are compared to calculations using the eikonal, direct reaction model, allowing $\ell$-assignments for the observed states. The lowest-lying resonance at an excitation energy of 1.48(4) MeV shows clear signs of a significant $\ell$=3-component, giving first evidence for $f_{7/2}$ single particle strength in $^{29}$Ne. The excitation energies and strengths of the observed states are compared to shell-model calculations using the sdpf-u-mix interaction