Nonradiative decay of the low-lying nuclear isomer 229m Th(3.5 eV) in a metal

A new nonradiative decay channel for the anomalously low-lying isomeric level 3/2 + (3.5±1.0 eV) of the 229 Th nucleus in a metal via the conduction electrons is examined. The lifetime of the isomer in a metal is calculated. An explanation is given for the experimental results of S. B. Utter et al. , Phys. Rev. Lett. 82 , 505 (1999), where the optical radiation spectrum of the indicated isomer was investigated.