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

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

12 pages, 14 figures, accepted for publication in Physical Review C