Self-consistent pairing calculations of the even Ca isotopes

Abstract

Hartree-Fock (HF) and Hartree-Fock-Bogolyubov (HFB) calculations have been performed for the even Ca isotopes. The nucleon-nucleon interaction is the semi-realistic Brink-Boeker force L 4 and the Coulomb force, no core is split off and the nuclei are allowed to assume axially symmetric and reflection invariant deformations. In HFB, only proton-proton and neutron-neutron pairing is considered. For all nuclei except 40Ca, two solutions, an oblate and a prolate one, are found; the prolate solution is the lowest in energy. Pairing among the pf shell neutrons turns out to be rather pronounced in the oblate states due to a high level density at the Fermi surface, which lowers the energy, widens the gap and makes the nucleus more spherical; it is weaker in the prolate states. Moreover, systematic variations with neutron excess are investigated such as symmetry energy, deformations and changes in the mass and charge distributions. The latter have been compared with those derived from electron scattering. Despite some over-all agreement, discrepancies are found in the details of the distributions, which indicate that the force without a spin-orbit interaction is not adequate for these nuclei.