γ -soft Ba146 and the role of nonaxial shapes at N≈90

Low-spin states in the neutron-rich, N = 90 nuclide ¹⁴⁶Ba were populated following β decay of ¹⁴⁶Cs , with the goal of clarifying the development of deformation in barium isotopes through delineation of their nonyrast structures. Fission fragments of ¹⁴⁶Cs were extracted from a 1.7-Ci ²⁵²Cf 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 β detectors, surrounded by a highly efficient high-purity Ge array. The new ¹⁴⁶Ba decay scheme now contains 31 excited levels extending up 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 γ degree of freedom.