Yrast Traps and Very High-Spin Yrast States inDy152

We have identified yrast states of ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ to spin ∼37, with unusually strong population of high-spin states in the (${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, $4n\gamma$) reaction. Yrast isomers with spins ∼17, 21, 27, and 31 were detected. For $I>~14$ the yrast states scatter about a straight line on an $E$ vs $I(I+1\mathrm{})\mathrm{}$ plot, consistent with predictions for aligned-particle configurations. The slope of the line yields an effective moment of inertia 18% larger than the rigid-sphere value. This and other arguments suggest possible oblate deformation at high spin.