Droplet models as approximations to the extended Thomas-Fermi method

Abstract

The conventional droplet model and the “ finite-range” droplet model of Möller et al. are compared with the extended Thomas-Fermi method (ETF) in order to test how reliably these models extrapolate from the region of known nuclei out to the neutron-drip line. We proceed by fitting each of the two droplet models to the binding energies of a large number of nuclei in the known region, calculated by the ETF method. On extrapolating to the neutron-drip line we find that the droplet models can disagree by as much as 10–15 MeV with ETF. However, a dramatic improvement results if higher-order surface-symmetry terms are included in the droplet model; their effect is to “soften” the neutron skin as the neutron excess grows.