Transition from Collective to Aligned-Particle Configurations at High Spin in Dy 154

The high-spin level structure of $^{154}\mathrm{Dy}$ has been determined through the ($^{34}\mathrm{S}$, $4n\ensuremath{\gamma}$) 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.