Description of high spin states

Abstract

This article is intended as a review of models describing high and very high spin states in nuclei. It further gives examples of the application of these models to data. (i) First, an outline of the cranked Hartree-Fock-Bogoliubov (CHFB) theory is given. It is applied to the first and the second anomaly of the moment of inertia normally called backbending (bb). (ii) The CHFB approach is extended to n quasi-particle (q.p.) states. The role of the odd protons for bb is investigated. (iii) The difficulties of the cranking model with the total angular momentum conserved only on the average are studied. (iv) An exact angular momentum conserving model in which valence nucleons in a vi 13 2 (or πh 11 2 ) shell are coupled to a core is introduced. It explains the oscillating behaviour of bb as a function of the neutron (or for second bb of the proton) number. (v) The decay of a highly excited and rapidly rotating compound nucleus after a heavy ion (HI) fusion reaction into particles and γ rays is described by the Monte Carlo method. Special attention is paid to the competition between collective and single particle γ ray decay. (vi) Different methods for calculating the deformation energy surface (DES) at high spins are discussed. The occurrence of yrast isomers is investigated. Furthermore, the nuclear stability against fission, particle emission and large scale shape changes is discussed.