Superdeformed shapes and configurations in thallium nuclei

Superdeformation studies in Tl-189,Tl-191,Tl-192 Gammasphere are discussed. New results on Tl-191 are the observation of interband transitions between the signature partner E2 bands and the measurement of an average quadrupole moment (Q(0) = 18 +/- eb) for these superdeformed structures. These data enable us to derive absolute M1 strengths and confirm that the 81(st) proton occupies the [642]5/2 orbital. Tentative data for one superdeformed sequence in Tl-189 are consistent with the prediction of a decrease in quadrupole deformation for the lightest nuclei at the limit of this island of superdeformation.