Studies of nuclei far from stability reveal trends among groups of neighboring nuclei where new and unexpected properties appear. One such region, the Island of Inversion near the N=20 shell gap, is home to nuclei with reordered single-particle energy levels compared to the spherical shell model. Studies of the 31Ne nucleus have revealed that its ground state has a halo component, characterized by a valence neutron orbiting a deformed 30Ne core. This lightly-bound nucleus with a separation... Show moreStudies of nuclei far from stability reveal trends among groups of neighboring nuclei where new and unexpected properties appear. One such region, the Island of Inversion near the N=20 shell gap, is home to nuclei with reordered single-particle energy levels compared to the spherical shell model. Studies of the 31Ne nucleus have revealed that its ground state has a halo component, characterized by a valence neutron orbiting a deformed 30Ne core. This lightly-bound nucleus with a separation energy of Sn=0.15(+0.16, -0.10)$~MeV is expected to have excited states that are neutron-unbound. This work presents a first study of the neutron-unbound excited states of 31Ne. Neutron-unbound states in 31Ne were populated in a two-proton knockout reaction from an 89 MeV/u 33Mg beam incident on a segmented Be reaction target. The 30Ne fragment and associated neutron from the decay of 31Ne* were detected by the MoNA-LISA-Sweeper experimental setup at the National Superconducting Cyclotron Laboratory. Invariant mass spectroscopy was used to reconstruct the two-body decay energy (30Ne+n).The two-body decay energy spectrum exhibits two features: a low-lying peak at 0.30 (+/- 0.17) MeV and a broad enhancement at 1.50 (+/- 0.33) MeV, each fit with an energy-dependent asymmetric Breit-Wigner line shape representing a resonance in the continuum. Accompanying shell model calculations combined with cross-section calculations using the eikonal reaction theory indicate that these features in the decay energy spectrum originate from multiple resonant states in 31Ne. Show less
