$\gamma$-soft $^{146}$Ba and the role of non-axial shapes at N ~ 90

TL;DR

This study investigates the shape evolution of neutron-rich $^{146}$Ba at N=90, revealing a gradual shape transition influenced by non-axial deformations, supported by new experimental decay data and IBA model comparisons.

Contribution

It provides the first detailed decay scheme of $^{146}$Ba with 31 levels and compares experimental results to theoretical models to understand shape changes at N=90.

Findings

$^{146}$Ba exhibits a more gradual shape transition at N=90 compared to Sm and Gd.

Enhanced $eta$-decay data extends the known excitation levels of $^{146}$Ba.

The IBA model suggests non-axial shapes play a significant role in this transition.

Abstract

Low-spin states in the neutron-rich, N = 90 nuclide $^{146}$Ba were populated following $\beta$-decay of $^{146}$Cs, with the goal of clarifying the development of deformation in Ba isotopes through delineation of their non-yrast structures. Fission fragments of $^{146}$Cs were extracted from a 1.7-Ci $^{252}$Cf source and mass-selected using the CARIBU facility. Low-energy ions were deposited at the center of a box of thin $\beta$ detectors, surrounded by a high-efficiency HPGe array. The new $^{146}$Ba 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 $\gamma$ degree of freedom.