The first-forbidden nonunique $\beta$ decay of ${}^{113m}\mathrm{Cd}$ was studied at the Gran Sasso underground laboratory of INFN with the help of a cadmium tungstate crystal scintillator enriched in ${}^{106}\mathrm{Cd}$ and contaminated by ${}^{113m}\mathrm{Cd}$ at level of $\approx$(14–28) Bq. The half-life of ${}^{113m}\mathrm{Cd}$ was determined through $\beta$ spectra analysis under low-background conditions recorded in 2009, 2015, and 2023, yielding $T_{1/2}=13.{61}_{-0.29}^{+0.22}$ yr. The isomeric transition branching ratio and the $\gamma$-ray energy for the ${}^{113m}\mathrm{Cd}$ decay to the ${}^{113}\mathrm{Cd}$ ground state were refined to 0.0790(21)% and 263.36(4) keV through ultralow-background $\gamma$-spectrometry using high-purity germanium (HPGe) detectors. The $\beta$-decay half-life limit for ${}^{113m}\mathrm{Cd}$ to the $1/2^{-}$ 391.699 keV metastable state of ${}^{113}\mathrm{In}$ was set for the first time as $T_{1/2}\ge 8.6\times {10}^6$ yr. The latter process was considered theoretically within the shell-model framework.

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• Beta decay
• Electroweak interactions in nuclear physics
• 90 ≤ A ≤ 149