The first excited isomeric state of 229Th possesses the lowest energy among all known excited nuclear states. The expected energy is accessible with today's laser technology and in principle allows for a direct optical laser excitation of the nucleus. The isomer decays via three channels to its ground-state (internal conversion, γ decay and bound internal conversion), whose strengths depend on the charge state of 229mTh. We report on the measurement of the internal-conversion decay half-life of neutral 229mTh. A half-life of 7 ± 1 μs has been measured, which is in the range of theoretical predictions and, based on the theoretically expected lifetime of ≈104 s of the photonic decay channel, gives further support for an internal conversion coefficient of ≈109, thus constraining the strength of a radiative branch in the presence of IC.
@article{arxiv.1801.05205,
title = {Lifetime measurement of the $^{229}$Th nuclear isomer},
author = {Benedict Seiferle and Lars von der Wense and Peter G. Thirolf},
journal= {arXiv preprint arXiv:1801.05205},
year = {2018}
}