Evidence for a Two-Phonon Octupole Vibrational Band inPu240

A rotational band with $K^{\pi }=0^{+}$ with $I=0\mathrm{}$ and $I=2\mathrm{}$ at excitation energies of 1410.8 and 1438.5 keV, respectively, has been identified and carefully characterized in ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$. We conclude that these states are members of a two-phonon octupole vibrational band.