Investigation of the anomalously low B(E2;41+→21+)/B(E2;21+→01+) ratio in Ce134 through lifetime measurements

Abstract

The existing experimental value of the ratio ${B}_{4/2}\ensuremath{\equiv}B(E2;{4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})/B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ in $^{134}\mathrm{Ce}$ is less than unity, which is outside the range allowed by current collective models and is highly anomalous. In the present work, new lifetime measurements of excited states in $^{134}\mathrm{Ce}$ have been performed in order to clarify this discrepancy. Excited states of $^{134}\mathrm{Ce}$ were populated by the fusion-evaporation reaction $^{122}\mathrm{Sn}(^{16}\mathrm{O},4n)^{134}\mathrm{Ce}$. The recoil distance doppler shift method was employed, and reliable lifetimes for the ${2}_{1}^{+}, {4}_{1}^{+}, {10}_{2}^{+}$, and ${12}_{2}^{+}$ states were derived from the differential decay curve method. The resulting ${B}_{4/2}$ value is larger than unity, resolving the disagreement with traditional collective models. The new experimental data is in very good agreement with the calculation in the framework of the interacting boson model. The systematic evolution in collectivity of the Ce isotopes is discussed.