Nuclear Shapes, Energy Gaps and Phase Transitions

Abstract

A survey is given of our current understanding of nuclear phase transitions caused by sharp changes in nuclear shapes and energy gaps. Phase diagrams and criteria for normal-superfluid-normal and spherical-prolate-oblate-spherical phase transitions are presented. The superfluid-normal phase transition and the associated "back-bending" phenomenon observed at high spins are discussed in some detail. The constrainted-Hartree-Bogolyubov treatment of the pairing-plus-quadrupole model, developed by the present author, explains the 50% increase in the moment of inertia of ¹⁶⁰Dy as J increases from 2 to 16, is capable of producing the back-bending effect, and predicts a Coriolis-Anti-Stretching effect at high spins.