Transition from Collective to Aligned-Particle Configurations at High Spin inDy154

The high-spin level structure of ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$ has been determined through the (${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$, $4n\gamma$) reaction. Lifetimes have been measured by use of the recoil-distance method. Both the level structure and lifetimes indicate a transition from collective to few-particle characteristics at high spin, possibly suggesting a changing shape from prolate through triaxial to oblate.