Half-life measurement of short-lived ~(94m)_(44) Ru~(44+) using isochronous mass spectrometry

摘要

Decay of the 8+ isomer in fully stripped ions ~(94)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)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)Ru~(44+) isomer decay. The isomeric half-life was deduced to be 102(17) μs, 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, ~(94)mRu~(44+) represents the shortest-lived nuclear state whose mass has ever been measured directly.