In a figure ( GIF figure of 5.9KB or PS figure of 21KB ), we show the potential energy curves for this nucleus obtained by solving the HF+BCS equation with constraint on the mass quadrupole moment Qz. The abscissa is the deformation parameter delta, while the ordinate is the energy without correction for the finite-mesh-size effect. The solid and the dot curves are calculated with the SIII force, the former with the standard-strength and the latter with a weaker paring correlation. The dash curve is calculated with the SkM* force, while the dot-dash curve with the SGII force (vertically shifted by 15 MeV).
The solid curve has as many as three minima, i.e., an oblate one at delta=-0.18, almost spherical one, and a prolate one at delta=0.41. Because the energies of these three minima are so close to each other (they are within 0.6 MeV), the order of the energies can be altered easily by changing the parameters of the interaction. With our chosen parameters, the oblate minimum has the lowest energy (solid curve). If one decreases the pairing gap by 25% (i.e., the average pairing gap with which to determine the pairing force strength is changed from 12 A-1/2 MeV to 9 A-1/2 MeV) the prolate minimum becomes the ground state (dot curve). Instead, by changing the Skyrme force parameter set to the SkM*, while using the standard pairing force strength, one can make the prolate minimum the ground state (dash curve). On the contrary, the SGII force deepens the spherical minimum (dot-dash curve). The shapes of nuclei in this mass region have been studied in many papers [GDG89,ZZ91,MGS92,KFP93].
We have also done calculations for 84Mo, in which the large prolate deformation solution (delta ~ 0.5) exists for the SIII and the SGII force but does not exist for the SkM* force.
