Search for two-phonon octupole excitations in 146Gd

The low-spin structure of the nearly spherical nucleus ¹⁴⁶Gd was studied using the ¹⁴⁴Sm(⁴He, 2n) fusion-evaporation reaction. High-statistics γ−γγ−γ coincidence measurements were performed at iThemba LABS with 7× 10⁹ γγ-γγ coincidence events recorded. Gated γγ-ray energy spectra show evidence for the 6+2→3−1→0+162+→31−→01+ cascade of E3 transitions in agreement with recent findings by Caballero and co-workers, but with a smaller branching ratio of Iγ=4.7(10)Iγ=4.7(10)for the 6+2→3−162+→31− 1905.1 keV γγ 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.