Evidence for an Octupole Rotational Band inSe74

Abstract

From in-beam $\gamma$-ray spectroscopy in ${}_{}{}^{74}{}_{}{}^{}\mathrm{Se}$, a negative-parity band to (${11}^{-}$) with rotational properties built on a $3^{-}$ collective octupole state is established along with the positive-parity (Barrette et al.) yrast band to (${14}^{+}$). The negative-parity band has essentially a constant moment of inertia in sharp contrast to the positive-parity band. This is the first negative-parity band outside those in deformed nuclei with such pure rotational behavior.