High-spin spectroscopy of 119,121I: Prolate and oblate shape coexistence.

Abstract

High-spin states in the odd-proton $^{119,121}\mathrm{I}$ isotopes have been studied following heavy-ion fusion-evaporation reactions using boron and carbon beams. Both prolate (\ensuremath{\gamma}=0\ifmmode^\circ\else\textdegree\fi{}) and oblate (\ensuremath{\gamma}=-60\ifmmode^\circ\else\textdegree\fi{}) collective bands have been observed built on low-lying positive- and negative-parity proton states, namely, ${\mathit{h}}_{11/2}$, ${\mathit{g}}_{9/2}$, ${\mathit{g}}_{7/2}$, and ${\mathit{d}}_{5/2}$ orbitals. At the highest spins (\ensuremath{\sim}39/2) the collective behavior of the ${\mathit{h}}_{11/2}$ yrast band is seen to break down when noncollective oblate states become yrast, resulting in the observation of band termination. The terminating state involves the \ensuremath{\pi}${\mathit{h}}_{11/2}$\ensuremath{\bigotimes}[\ensuremath{\pi}${\mathit{g}}_{7/2}$${]}^{2}$\ensuremath{\bigotimes}[\ensuremath{\nu}${\mathit{h}}_{11/2}$${]}^{2}$ configuration at \ensuremath{\gamma}=+60\ifmmode^\circ\else\textdegree\fi{}.