Neutral $s$ States in Loosely Bound Nuclei

Abstract

In reviewing the data that has accumulated in light nuclei we find that the binding energy plays a critical role in describing the variation in energy of $s$ states relative to other states. The behavior of states with zero angular momentum within a few MeV of threshold is qualitatively different from that of neutron states with any other $\ell$ value or of any proton state. This observation is explored for simple Woods-Saxon potentials and is remarkably successful in describing a wealth of experimental data for nuclei with neutron numbers between 5 and 10. The lingering of neutron $s$ states just below threshold is associated with the increases in radii of the neutron density distributions, the neutron halos, and leads to speculations about possible halos in heavier nuclei.

Minor revisions, 5 pages, 5 figures, published in Physical Review C