High-spin states in ${}^{161}\mathrm{Er}$ have been studied experimentally using the ${}^{150}\mathrm{Nd}$(${}^{16}\mathrm{O}$,5$\mathit{n}$) reaction at a beam energy of 86 MeV. The $5/2^{+}[642]$, $3/2^{-}[521]$, and $11/2^{-}[505]$ bands are extended up to high-spin states, and particularly the $\alpha =-1/2$ branch of the ground state $3/2^{-}[521]$ band is revised significantly. The relatively enhanced $E1$ transitions from the $3/2^{-}[521]$ band to the $5/2^{+}[642]$ band are observed. The band properties are analyzed within the framework of a triaxial particle-rotor model, and near-prolate shape and triaxial deformation are proposed to the $3/2^{-}[521]$ and $5/2^{+}[642]$ bands, respectively. Signature inversion occurs in the $3/2^{-}[521]$ band after the band crossing in ${}^{161}\mathrm{Er}$, and the systematics of the signature inversion associated with the $3/2^{-}[521]$ configuration are discussed. By analyzing the properties of the relatively enhanced $E1$ transitions, it is found that the $R(E1/E2)$ values show angular momentum dependence before the band crossing, and these enhanced $E1$ transitions could be attributed to octupole softness.

• Received 13 September 2010

DOI:https://doi.org/10.1103/PhysRevC.83.034318