New features of collective nuclear rotation at very high frequency inSb109

Three rotational bands have been discovered in the nucleus ${}_{}{}^{109}{}_{}{}^{}\mathrm{Sb}$ that extend in angular momentum to ≃81/2ħ. The rotational frequency at the highest spins reaches ħω≃1.4 MeV, the highest frequency so far observed in a heavy nucleus. With increasing frequency the collective moments of inertia of all three bands smoothly diminish to unexpectedly low values, ${\mathit{scrJ}}^{\mathrm{}\left(2\right)\mathrm{}}$∼13${\mathrm{ħ}}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$, approximately one-third the rigid-body value, and, contrary to expectations, the moments of inertia become nearly equal to one another and to those of rotational bands in the core nucleus ${}_{}{}^{108}{}_{}{}^{}\mathrm{Sn}$.