Spectroscopy of Cd113m

The first-forbidden nonunique beta decay of 113⁢mCd was studied at the Gran Sasso underground laboratory of INFN with the help of a cadmium tungstate crystal scintillator enriched in 106Cd and contaminated by 113⁢mCd at level of approximately equal to (14–28) Bq. The half-life of 113⁢mCd was determined through beta spectra analysis under low-background conditions recorded in 2009, 2015, and 2023, yielding T1/2=13.61+0.22−0.29 yr. The isomeric transition branching ratio and the gamma-ray energy for the 113⁢mCd decay to the 113Cd 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 113⁢mCd to the 1/2− 391.699 keV metastable state of 113In was set for the first time as T1/2≥8.6×106 yr. The latter process was considered theoretically within the shell-model framework.