Search For Low-Spin Superdeformed States In Nuclei

Since the first discovery in 1986 of a rotational band at high angular momentum with deformation parameters near beta = 0.6, a great deal of research has been devoted to the study of these superdeformed (SD) bands in nuclei leading to the identification of similar bands in numerous nuclei in the mass 130, 150, and 190 regions. While superdeformed shape isomers have been observed at low spin in the actinides via spontaneous fission and in a few cases via gamma decay, below mass 200 the low-spin members of the SD bands have not been observed. Theoretical calculations are able to account for the relative stability of the superdeformed bands in the nuclei where they have been observed. These calculations suggest that in the Hg-Pb region the SD shape should be stable at a rotational frequency of 0. Several experiments have been performed to search for the population and decay of the lower spin members of the SD bands in the mass 190 region and some are still in progress. To this date, none has provided conclusive observation of the 0+ bandhead of a superdeformed band. The experimental techniques utilized in several of these are described.