The ${}^{114}\mathrm{Cd}({}^{48}\mathrm{Ca},6n\gamma )$ reaction at 215 MeV has been investigated using the Gammasphere spectrometer to study the high-spin structure of the nucleus ${}_{68}^{156}{\mathrm{Er}}_{88}$. Many new transitions have been established along with definitive spin-parity level assignments from a high-fold angular-distribution analysis. In addition, absolute $B(M1)$ and $B(E1)$ strengths have been inferred from measured $\gamma$-ray branching ratios. Strong $B(E1)$ strength (${10}^{-3}$ W.u.) is discussed in terms of possible octupole collectivity at low spin. At high spin, this nucleus undergoes a Coriolis-induced shape transition from a prolate state of collective rotation to a noncollective, triaxial-oblate configuration. The yrast positive-parity structure ultimately terminates in an energetically favored oblate state at $I^{\pi }={42}^{+}$. Several weak high-energy $\gamma$-ray transitions have been discovered that feed this favored state. State-of-the-art cranked Nilsson-Strutinsky calculations are used to interpret the high-spin behavior of ${}^{156}\mathrm{Er}$ and comparisons are made with other $N=88$ isotones.

• Received 5 February 2009

DOI:https://doi.org/10.1103/PhysRevC.79.044324