Nuclear structure at high and very high spin: theoretical description

First, classical rotation is studied. Then cranking procedure is analyzed as a tool to investigate nucleonic orbits in a rotating nuclear potential. Energies and alignments in nucleonic orbits are discussed in terms of angular velocity ω. The potential energy surfaces are calculated and discussed for any (fixed) value of angular momentum. Some predictions concerning the possible onset of a superdeformed phase are given. Then, the structure of nuclear rotation is examined in the presence of the short-range pairing forces that generate the superfluid correlations in the nucleus. Examples of the Bengtsson-Frauendorf plots (quasiparticle energies versus angular velocity of rotation) are given and discussed. The backbending phenomenon is analysed in terms of band crossing. The dependence of the crossing frequency on the pairing-force strength is discussed. Possibilities of the role of new components in the two-body force (quadrupole-pairing) are considered. Possibilities of the phase transition from superfluid to normal states in the nucleus are analysed. The role of the second (dynamic) moment of inertia in this analysis is discussed. In spherical or weakly deformed nuclei (mostly oblate) angular momentum is aligned parallel to the nuclear symmetry axis. Rotation is of non collective origin in this case. The motion is best analysed by representing nuclear single-particle energies as points in the (m,e) plane. Examples of the analysis of nuclear spectra in this case (exhibiting also the isomeric states called yrast (traps)) are given. Possible forms of the collective excitations superimposed on top of the high-spin states are discussed. In particular, the giant resonance excitations formed on top of the high-spin states are considered and their properties discussed