Models for Rotating Nuclei - Cranking and Rotor + Particles Coupling

Abstract: This dissertation investigates properties of rotating atomic nuclei. Studies are performed using the cranking model and in the particles + rotor model. Properties studied are energy spectra and electromagnetic transition probabilities. The thesis also investigates the use of different liquid drop models at high spin values and studies the use of the particle + rotor approximation for the description of different 'exotic' ways of rotating. The dissertation comprises six original papers, which are presented following an introduction to the fields of research and the methods used and the systems studied. Paper I investigates the use of different meanfield parameters for the description of experimental high-spin states in 86Nb. A better agreement with experimental data could be found, however some experimental features proved hard to explain. In Paper II new experimental data on high-spin states in 58Ni was presented and compared with cranking calculations. A good agreement with calculation led to a clear interpretation of all observed states. The interaction and transitions between two of the rotational bands are analyzed and found to be sensitive to the deformation of the nucleus. In Paper III the average pairing energy is removed from the parameters of the liquid-drop model by performing a refitt to nuclear groundstate masses. The modified model is then used to calculate the total energy of the nucleus at high-spin values. Two different models are compared and one is found to be more reliable for light nuclei. In Paper IV the usual particle plus rotor model is extended to incorporate an arbitrary number of particles coupled to the rotor. This model is then used to describe the so called shears bands where states are formed by the coupling of perpendicular neutron and proton spin vectors. The same model is employed in Paper V for the description of collective wobbling excitations in nuclei. In Paper VI, new experimental data on quadrupole transitions in 142Gd are presented. These data are compared to the result of cranking calculations employing a monopole pairing interaction. Based on the calculations the relatively small transition probabilities are interpreted as being the result of the rotation taking place around the longest principal axis of the mass distribution.