Influence of shell effects and stable octupole deformation on the<i>E</i>1 and<i>E</i>2 transition rates in the heavy-Ba region

Lifetimes were measured for the ${2}_{1}^{+}$, ${4}_{1}^{+}$, ${0}_{2}^{+}$, ${1}_{1}^{\mathrm{\ensuremath{-}}}$, and ${3}_{1}^{\mathrm{\ensuremath{-}}}$ levels in $^{142,144,146}\mathrm{Ba}$ using a recently developed \ensuremath{\beta}-\ensuremath{\gamma}-\ensuremath{\gamma} 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 $^{146}\mathrm{Ba}$.

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