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

Le résumé fourni par la source

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, $^{148,150}\mathrm{Ba}$, has been studied via $\ensuremath{\beta}$ decay at the ISOLDE Decay Station. This paper reports on the first measurement of the positive- and negative-parity low-spin excited states of $^{150}\mathrm{Ba}$ and presents an extension of the $\ensuremath{\beta}$-decay scheme of $^{148}\mathrm{Cs}$. Employing the fast timing technique, half-lives for the ${2}_{1}^{+}$ level in both nuclei have been determined, resulting in ${T}_{1/2}=1.51(1)$ ns for $^{148}\mathrm{Ba}$ and ${T}_{1/2}=3.4(2)$ ns for $^{150}\mathrm{Ba}$. The systematics of low-spin states, together with the experimental determination of the $B(E2:{2}^{+}\ensuremath{\rightarrow}{0}^{+})$ transition probabilities, indicate an increasing collectivity in $^{148\text{--}150}\mathrm{Ba}$, 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.

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