Lifetime measurements inRe166: Collective versus magnetic rotation

Abstract

Lifetimes of excited states in the neutron-deficient odd-odd nucleus $^{166}\mathrm{Re}$ have been measured for the first time using the recoil distance Doppler-shift method. The measured lifetime for the $({8}^{\ensuremath{-}})$ state; $\ensuremath{\tau}=480$ (80) ps, enabled an assessment of the multipolarities of the $\ensuremath{\gamma}$ rays depopulating this state. Information on electromagnetic transition strengths were deduced for the $\ensuremath{\gamma}$-ray transitions from the $({9}^{\ensuremath{-}}),\phantom{\rule{0.16em}{0ex}}({10}^{\ensuremath{-}})$, and $({11}^{\ensuremath{-}})$ states, and in the case of the $({10}^{\ensuremath{-}})$ and $({11}^{\ensuremath{-}})$ states limits on the $B(M1)$ and $B(E2)$ strengths were estimated. The results are compared with total Routhian surface predictions and semiclassical calculations. Tilted-axis cranking calculations based on a relativistic mean-field approach (TAC-RMF) have also been performed in order to test the possibility of magnetic rotation in the $^{166}\mathrm{Re}$ nucleus. While the TAC-RMF calculations predict a quadrupole-deformed nuclear shape with similar ${\ensuremath{\beta}}_{2}$ deformation as obtained by using the TRS model, it was found that the experimental electromagnetic transition rates are in better agreement with a collective-rotational description.