Speaker
Description
Lifetimes of the low-lying excited states in the yrast bands of $^{93}$Ru and $^{94}$Ru were measured using the $\gamma$-$\gamma$-$\Delta T$ method. The experiment was carried out at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. The $^{93}$Ru and $^{94}$Ru were produced by in-flight fragmentation of a $^{124}$Xe primary beam, impinging on a $^9$Be target. These ions were transported through the BigRIPS and Zero Degree Spectrometer (ZDS) and implanted into a segmented plastic-based active stopper at F11, one of the focal positions. The $\gamma$ rays emitted from the isomeric decays were detected by the IDATEN (International Detector Assembly for fast-Timing measurements of Exotic Nuclei) array, which consists of 48 LaBr3(Ce) detectors.
Recent studies have reported the anomalous enhancement of the reduced transition probabilities for the $4^{+} \to 2^{+}$ transition in $^{94}$Ru, compared to the theoretical prediction based on the large-scale shell model with partial seniority conservation. This enhancement has been attributed to a small mixing of $\nu$ = 4 and 2 seniorities. However, the previous results are inconsistent, and the additional high-precision experimental data are required to better understand the seniority mixing. In this presentation, we report new level lifetime values for $^{93}$Ru and $^{94}$Ru and discuss their implications for the seniority symmetry breaking.
