The spectroscopy of 183Tl:an extreme case of prolate-oblate shape-competition

The yrast sequence in 183Tl has been studied for the first time in recoil-mass and decay tagged γ-ray spectroscopic measurements. A rotational-like cascade of seven transitions is observed down to the bandhead with spin 13/2+. In contrast to adjacent nuclei, links from the yrast band to a lower lying weakly deformed (oblate) structure are not observed. It appears that the prolate energy minimum in 183Tl drops significantly compared to 185Tl and minimizes below the neutron i13/2 midshell (N⩽102). Possibilities for the decay out of the band in 183Tl are discussed.