Half-life measurement of short-lived Ru44+4494m using isochronous mass spectrometry

Abstract

Decay of the ${8}^{+}$ isomer in fully stripped ions $^{94}\mathrm{Ru}^{44+}$ is observed during its circulation in the experimental Cooler Storage Ring (CSRe) at the Heavy Ion Research Facility in Lanzhou (HIRFL). The $^{94}\mathrm{Ru}^{44+}$ ions were produced via projectile fragmentation and stored in CSRe tuned into the isochronous ion-optical mode. The timing signals of the ions, passing through a time-of-flight detector, were consecutively registered and used to determine the variation of revolution time as a function of revolution number. A sudden change of the revolution time at a specific revolution was identified as a fingerprint of the $^{94}\mathrm{Ru}^{44+}$ isomer decay. The isomeric half-life was deduced to be 102(17) $\ensuremath{\mu}\mathrm{s}$, which agrees well with the theoretical expectation by blocking the internal conversion decay of the isomer. Our work proved the feasibility of studying decays of short-lived isomers in high atomic charge states using the isochronous mass spectrometry. In addition, $^{94m}\mathrm{Ru}^{44+}$ represents the shortest-lived nuclear state whose mass has ever been measured directly.