We report on a study of the $\alpha$-decay fine structure and the associated $E_{\alpha }-E_{\gamma }$ correlations in the decays of ${}^{171,172}\mathrm{Os}$ and ${}^{171,172,174}\mathrm{Ir}$. In total, 13 new $\alpha$-decay energy lines have been resolved, and three new $\gamma$-ray transitions have been observed following the new decay branches to ${}^{168}\mathrm{Re}$ and ${}^{167}\mathrm{W}$. The weak $\alpha$-decay branch from the bandhead of the $\nu i_{13/2}$ band in ${}^{171}\mathrm{Os}$ observed in this work highlights an unusual competition between $\alpha , \beta$, and electromagnetic decays from this isomeric state. The nucleus ${}^{171}\mathrm{Os}$ is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in ${}^{92}\mathrm{Mo}({}^{83}\mathrm{Kr},xpyn$) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt $\gamma$-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that $\alpha$-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.

• Received 13 October 2022
• Accepted 11 January 2023

DOI:https://doi.org/10.1103/PhysRevC.107.014308

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Published by the American Physical Society