Search for two-phonon octupole excitations in ¹⁴⁶Gd

Abstract.

The low-spin structure of the nearly spherical nucleus ¹⁴⁶Gd was studied using the ¹⁴⁴Sm(⁴He, 2n) fusion-evaporation reaction. High-statistics $\gamma - \gamma$ coincidence measurements were performed at iThemba LABS with 7× 10⁹ $\gamma$-$\gamma$ coincidence events recorded. Gated $\gamma$-ray energy spectra show evidence for the $6^{+}_{2} \rightarrow 3^{-}_{1} \rightarrow 0^{+}_{1}$ cascade of E3 transitions in agreement with recent findings by Caballero and co-workers, but with a smaller branching ratio of $I_{\gamma} = 4.7(10)$ for the $6^{+}_{2} \rightarrow 3^{-}_{1}$ 1905.1 keV $\gamma$ ray. Although these findings may support octupole vibrations in spherical nuclei, sophisticated beyond mean-field calculations including angular-momentum projection are required to interpret in an appropriate way the available data due to the failure of the rotational model assumptions in this nucleus.