The multiplicity of shapes in t 1 nuclei

Thallium nuclei (Z = 81) provide a rich laboratory for the study of nuclear shapes. In spite of the location adjacent to a closed shell number of protons (Pb 2 = 82), T1 nuclei exhibit an impressive array of excitations built on different shapes, prolate and oblate, normal and superdeformed. The properties of these various modes of excitation present challenges to nuclear models and spur interest in understanding the configurations involved. Furthermore, the richness of structures built upon different shapes and different configurations gives a good opportunity in future measurements to understand new questions that have arisen, e.g. the conditions under which discrete lines might be observed for direct one-step decay from superdeformed to low-lying bands of normal deformation. This paper describes some of the recent measurements on rotational bands associated with normal and superdeformed shapes in TI isotopes. We have been involved in a series of experiments which lead to the assignment of rotational bands in the following nuclei: