Semi-infinite matter and the nuclear surface

The surface energy and thickness of semi-infinite nuclear matter are calculated by Swiatecki's variational method. Smooth, effective two-body interactions are used to study the relationship between the characteristics of each interaction and the predicted bulk surface properties. Both local and non-local Gaussian interactions are considered and are adjusted to either saturate infinite nuclear matter or to fit two-nucleon (singlet-even) phase shifts. Purely local potentials are found to give an excessively large surface energy ( ), whereas potentials having some non-locality (even if the non-locality is confined to short distances) reduce the surface energy to a reasonable value of (20–30) . The separate potential and kinetic energy contributions are examined in detail and are used to explain how the character of each interaction affects the surface properties. This model calculation shows that the surface energy is greatly influenced by non-locality. Also, we find that the predicted surface thickness tends to be too large (t ≈ 3.5 fm) for potentials that are adjusted to saturate and too small (t ≈ 1.8 fm) for potentials that are fitted to two-nucleon phase-shifts.