Deviations from axial symmetry in181Os

Lifetimes of rotational states built on the ${7/2}^{\ensuremath{-}}[514]$ and ${1/2}^{\ensuremath{-}}[521]$ Nilsson single-particle orbitals in ${}^{181}\mathrm{Os}$ have been measured using the coincidence recoil-distance method. The experimentally determined quadrupole moment, assuming axial symmetry, is $\ensuremath{\approx}20%$ larger for the ${7/2}^{\ensuremath{-}}[514]$ band compared with the ${1/2}^{\ensuremath{-}}[521]$ band. The difference can be understood as an effect of triaxiality. Total Routhian surface calculations show deviations from axial symmetry for both bands, leading to good agreement between theory and experiment.