Influence of shell effects and stable octupole deformation on theE1 andE2 transition rates in the heavy-Ba region

Lifetimes were measured for the $2_1^{+}$, $4_1^{+}$, $0_2^{+}$, $1_1^{\mathrm{-}}$, and $3_1^{\mathrm{-}}$ levels in ${}_{}{}^{142,144,146}{}_{}{}^{}\mathrm{Ba}$ using a recently developed β-γ-γ fast timing method. In ${}_{}{}^{146}{}_{}{}^{}\mathrm{Ba}$, the ${\mathit{Q}}_0$ moment for the negative parity band was slightly larger than that for the positive parity band. The isovector E1 rates which were very small in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Ba}$ and large in ${}_{}{}^{144}{}_{}{}^{}\mathrm{Ba}$ can be explained in terms of shell effects on the electric dipole moment. The new data are interpreted by both the spdf interacting boson and the reflection-asymmetric deformed shell models and provide compelling evidence for a static octupole deformation near ${}_{}{}^{146}{}_{}{}^{}\mathrm{Ba}$.