Single- and Double-Octupole Excitations inGd148

In the two-valence-neutron nucleus ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$, in-beam ${}_{}{}^{148}{}_{}{}^{}\mathrm{Sm}(\alpha ,4n)$ and (${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$3n$) measurements have identified nine ${\nu }^2\times \mathrm{octupole}$ levels with $3<I<\mathrm{}14\mathrm{}$. The measured half-life of the ${(\nu f_{\frac{7}{2}}^2\times 3^{-})}_{9^{-}}$ state gives $B(E3,9^{-}\to 6^{+})=55\mathrm{}\mathrm{}\left(6\right)\mathrm{}{B}_{\mathrm{W}}$. A high-lying ${12}^{+}$ level, which decays by $E3\mathrm{}$ to the $9^{-}$ state, as well as a ${14}^{+}$ level are shown to be two-phonon octupole excitations of stretched ${\nu }^2\times 3^{-}\times 3^{-}$ character. All these results can be quantitatively derived from the experimental data for the coupling of one neutron to the core octupole observed in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$.