Superdeformed nuclei

Abstract

The concept of the superdeformed shape is first introduced classically as the most stable configuration of a rapidly rotating deformable body and is then applied to nuclei. The shape of nuclei are determined by a competition between the collective energy of the core, to which classical considerations apply quite well, and the quantal energies of the valence nucleons, which may be evaluated by the Nilsson model. The result of this competition is that slowly rotating nuclei can be either oblate or prolate but rapidly rotating nuclei can have a superdeformed prolate shape, with a 2:1 ratio of axes particularly favoured.

The evidence for superdeformation in nuclei is described under four headings. Firstly, some light nuclei are superdeformed in their ground state or in an excited state. Secondly, some nuclei pass through a well defined superdeformed shape on the way to fission. Thirdly, studies of the excitation functions of elastic and inelastic scattering of identical heavy ions provide evidence of a nuclear molecule in a superdeformed shape. Finally, recent analyses of gamma rays from nuclei formed in a very high spin state by a heavy ion collision provide conclusive evidence for superdeformation.