Flow patterns for collective quadrupole vibrations in heavy nuclei

By means of the adiabatic cranking model the properties of the current and velocity fields of nuclear quadrupole vibrations for even-even nuclei in the rare-earth region are investigated. BCS correlated wave functions based on the Nilsson single-particle hamiltonian have been used. The current fields are analyzed in terms of vector spherical harmonics. The realistic microscopic currents show a vortex structure not present in the classical irrotational flow. The microscopic origin of the vortex structure is investigated. Whereas irrotational flow is related to high-lying excitations, the vortical current is shown to represent low-lying excitations. The influence of pairing is demonstrated; high pairing gaps yield nearly irrotational flow. The effect of deformation is studied. The cranking-model velocity fields are compared with the results of classical first and zero sound calculations and are found to agree with the latter in important aspects. (orig.)