gamma-soft Ba-146 and the role of nonaxial shapes at N approximate to 90

Low-spin states in the neutron-rich, N = 90 nuclide Ba-146 were populated following beta decay of Cs-146, with the goal of clarifying the development of deformation in barium isotopes through delineation of their nonyrast structures. Fission fragments of Cs-146 were extracted from a 1.7-Ci Cf-252 source and mass selected using the CAlifornium Rare Ion Breeder Upgrade (CARIBU) facility. Low-energy ions were deposited at the center of a box of thin beta detectors, surrounded by a highly efficient high-purity Ge array. The new Ba-146 decay scheme now contains 31 excited levels extending up to similar to 2.5 MeV excitation energy, double what was previously known. These data are compared to predictions from the interacting boson approximation (IBA) model. It appears that the abrupt shape change found at N = 90 in Sm and Gd is much more gradual in Ba and Ce, due to an enhanced role of the gamma degree of freedom.