Evolution of deformation in neutron-rich Ba isotopes up to A=150

The occurrence of octupolar shapes in the Ba isotopic chain was recently established experimentally up to N=90. To further extend the systematics, the evolution of shapes in the most neutron-rich members of the Z=56 isotopic chain accessible at present, 148,150Ba, has been studied via β decay at the ISOLDE Decay Station. This paper reports on the first measurement of the positive- and negative-parity low-spin excited states of 150Ba and presents an extension of the β-decay scheme of 148Cs. Employing the fast timing technique, half-lives for the 2+1 level in both nuclei have been determined, resulting in T1/2=1.51(1) ns for 148Ba and T1/2=3.4(2) ns for 150Ba. The systematics of low-spin states, together with the experimental determination of the B(E2:2+→0+) transition probabilities, indicate an increasing collectivity in 148–150Ba, towards prolate deformed shapes. The experimental data are compared to symmetry conserving configuration mixing (SCCM) calculations, confirming an evolution of increasingly quadrupole deformed shapes with a definite octupolar character.status: publishe