Existence of proton halos near the drip line

Abstract

The proton drip-line nucleus ${}_{}{}^{17}{}_{}{}^{}\mathrm{Ne}$ is studied in a three-body model of ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ plus two protons. The ${}_{}{}^{17}{}_{}{}^{}\mathrm{Ne}$ nucleus has a Borromean binding structure, and calculations show a rms matter radius of 2.77–2.81 fm, in agreement with experiment. The model gives a proton radius excess about 0.26–0.32 fm over the neutron radius, showing that a proton skin is present. The 73% probability of a valence proton being outside the rms core radius is sufficiently large, however, to indicate a halo. Predictions for the momentum distributions of ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ fragments are given, and these, if verified, would also suggest a two-proton halo structure for ${}_{}{}^{17}{}_{}{}^{}\mathrm{Ne}$. This would be the first identification of a two-proton halo nucleus.