Electromagnetic Properties of Nuclei at High Spins

Abstract

A photon emitted by an excited state is likely to carry away, at most, 1 or 2ft of angular momentum. Therefore, a profusion of photons is needed to deexcite the rapidly rotating states of nuclei formed by heavy-ion reactions. The study of electromagnetic properties has become the primary source of information on nuclear structure at high spins and, also, at the warm temperatures present in the initial stage of the electromagnetic cascade process. The purpose of this paper is a review of the E1, M1, and E2 properties of such highly excited states, in order to set the stage with theoretical props for the section on this topic in the present volume. This review does not aspire to completeness or a fair distribution of credit for past achievements, but does attempt to highlight the major current research topics in the field. A chart of these topics in the plane of energy versus angular momentum is given in Fig. 1. They involve both the properties of the rotating but “cold” states on or near the yrast line, which can be experimentally resolved as discrete states, and of the increasingly closely spaced levels at higher temperature. The former reveal the response of nuclear structure to rotation, and the latter provide unique insight into the transition of a quantum system from order to chaos.