Lifetime measurement in Ru94 and Tc93 to investigate seniority conservation in the N=50 isotones

Abstract

Low-lying excited states in ${}^{93}\mathrm{Tc}$ and ${}^{94}\mathrm{Ru}$ were populated using the two fusion-evaporation reactions ${}^{90}\mathrm{Zr}({}^6\mathrm{Li},3n){}^{93}\mathrm{Tc}$ and ${}^{92}\mathrm{Mo}(\alpha ,2n){}^{94}\mathrm{Ru}$ at the Cologne FN Tandem accelerator and their lifetimes were measured using a hybrid setup of high-purity germanium and fast cerium doped lanthanum bromide detectors for $\gamma \text{−}\gamma$ fast-timing. The measured lifetimes fill gaps in the experimental data for electromagnetic transition probabilities $B\left(\sigma \lambda \right)$ along the $N=50$ isotonic chain and provide more insight for ambiguous cases, such as the lifetime of the $4_1^{+}$ state in ${}^{94}\mathrm{Ru}$. The experimental data are compared with theoretical $B\left(E2\right)$ values from a single-$j$ approximation, with state-dependent effective charges derived from ${}^{92}\mathrm{Mo}$ and with the results from shell-model calculations performed using the SR88MHJM interaction in the $\pi (1p_{1/2},0g_{9/2})$ model space.