Necked-in Superdeformed Nuclei

Sammanfattning: Superdeformation, i.e. elongated shapes with the longest axis approximately twice as long as the shorter axes, has provided many new insights in nuclear structure. In this dissertation the possibility of forming superdeformed states related to two connected spheres, having a more or less pronounced neck, is investigated. Detailed Nilsson-Strutinsky calculations with the cranked Woods-Saxon potential and a finite-range liquid drop model are carried out in the 180Hg region, where superdeformed states related to two overlapping 90Zr are predicted. Detailed spectroscopic properties are calculated. The effect of the necking degree of freedom on the the giant dipole resonance, GDR, is investigated. The calculations are carried out with the Woods-Saxon potential for the single-particle states, and the random phase approximation formalism for the phonon states. The residual interaction and coupling constants are determined by requirements of translational invariance. The lower energy component of the GDR spectrum for superdeformed shapes, corresponding to vibrations along the symmetry axis, is diminished with increasing necking, and the mean energy of the GDR is increased. The folded Yukawa-plus-exponential liquid drop models take into account the finite range of the nuclear force, which is important when elongated and necked-in nuclear shapes are considered. However, it is shown that they are unstable towards higher multipole deformations, and that unphysical shapes are obtained in free minimizations when too high multipole deformations are included. Limits on multipolarity are given as functions of mass number.