Matrix element of the anomalously low-energy (3.5±0.5 eV) transition in 229Th and the isomer lifetime

The matrix element of the anomalously low-energy (3.5±0.5 eV) nuclear M 1 transition between the first excited state and the ground state of the 229 Th nucleus is determined with allowance for the Coriolis mixing of the rotational bands. The upper and lower limits on the lifetime of the level with respect to an isomeric transition are given. A method is proposed for measuring the half-life of the low-lying isomer 229 m Th directly in a 233 U sample.