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.