Abstract
Recent reaction measurements have been interpreted as evidence of a halo structure in the exotic
neutron-rich isotopes 29,31Ne. While theoretical studies of 31Ne generally agree on its halo nature, they
differ significantly in their predictions of its properties and underlying cause (e.g., that 31Ne lies in an
"island of inversion'"). We have made a systematic theoretical analysis of possible Neon halo signatures --
the first using a fully microscopic, relativistic mean field approach that properly treats positive energy
orbitals (such as the valence neutron in 31Ne) self-consistently with bound levels, and that includes
the pairing effect that keeps the nucleus loosely bound with negative Fermi energy. Our model is the analytical continuation of the coupling constant (ACCC) method based on a relativistic mean field
(RMF) theory with Bardeen-Cooper-Schrieffer (BCS) pairing approximation. We calculate
neutron- and matter-radii, one-neutron separation energies, p- and f-orbital energies and occupation probabilities, and neutron densities for single-particle resonant orbitals in 27-31Ne. We analyze these results for evidence of neutron halo formation in 29,31Ne. Our model predicts a p-orbit 1n halo structure for 31Ne, based on a radius increase from 30Ne that is 7 - 8 times larger than the increase from 29Ne to 30Ne, as well as a decrease in the neutron separation energy by a factor of ~ 10 compared to that of 27-30Ne. In contrast to other studies, our inclusion of resonances yields an inverted ordering of p and f orbitals for small deformations. Furthermore, we find no evidence of an s-orbit 1n halo in 29Ne as recently claimed in the literature.
