Direct lifetime measurements via $\gamma \text{−}\gamma$ coincidences using a fast timing detector array consisting of ${\mathrm{LaBr}}_3\left(\mathrm{Ce}\right)$ scintillators has been applied to determine the lifetime of low-lying states in the semimagic $(N=50)$ nucleus ${}^{94}\mathrm{Ru}$. The experiment was carried out as the first in a series of “FAIR-0” experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in ${}^{94}\mathrm{Ru}$ were populated primarily via the $\beta$-delayed proton emission of ${}^{95}\mathrm{Pd}$ nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon ${}^{124}\mathrm{Xe}$ beam impinging on a 4 g/${\mathrm{cm}}^2{}^9\mathrm{Be}$ target. While the deduced $E2$ strength for the $2^{+}\to 0^{+}$ transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate $4^{+}\to 2^{+}$ transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the $fpg$ proton hole space with respect to doubly magic ${}^{100}\mathrm{Sn}$. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority $\nu =2$, $I^{\pi }=4^{+}$ state and that of a close-lying $\nu =4$ state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive $6^{+}\to 4^{+}$ transition can be attributed to the same mechanism but with a destructive interference. It is noted that such effects may provide stringent tests of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations.

• Received 17 October 2021
• Revised 17 January 2022
• Accepted 11 March 2022

DOI:https://doi.org/10.1103/PhysRevC.105.L031304

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