6533b859fe1ef96bd12b7631

RESEARCH PRODUCT

Prolate yrast cascade in183Tl

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The yrast sequence in ${}^{183}\mathrm{Tl}$ has been studied for the first time in recoil-mass selected \ensuremath{\gamma}-ray spectroscopic measurements. A rotational-like cascade of seven transitions is established down to the band head with probable spin and parity ${(13/2}^{+}).$ Unlike in the adjacent odd-mass Tl nuclei, prompt \ensuremath{\gamma} decay from the yrast band to a lower lying weakly deformed (oblate) structure is not observed. These features are consistent with the predicted drop of the prolate band head in ${}^{183}\mathrm{Tl}$ compared to ${}^{185}\mathrm{Tl}.$ The implications for the prolate energy minimum in odd-mass Tl nuclei at the neutron ${i}_{13/2}$ midshell $(N=103)$ are discussed.