Details of nuclear masses away from stability: pairing and deformation effects

Abstract

Exact many-body calculations have been performed in a large Nilsson-model basis using a two-body monopole-pairing force. The diagonalisations are reduced to a manageable size by exploiting the symmetry of the general pairing Hamiltonian and time-reversal invariance. The results have been successfully applied to a study of multi-quasiparticle states in the Hf-W region. An extension of this work, calculating nuclear masses, allows a comparison with the experimental neutron-pairing energiesP _N. These have been studied in detail for the Kr isotopes. Two important conclusions emerge (i) the monopole-pairing term must be generalized to a state-dependent interaction; good results being obtained for a delta-function force (ii) the small nuclear deformations relevant to this mass region appear to vary smoothly, as given by laser spectroscopy experiments, rather than showing the fluctuations of microscopic-macroscopic calculations.