Lifetime measurement of the internal conversion decay channel of ^229mTh

Among all so far known excited nuclear states, the first isomeric state of ²²⁹Th exhibits the lowest excitation energy, which has been reported to be 7.8±0.5 eV. This energy range is accessible with today's laser technology and could allow for a direct nuclear laser excitation. However, at present, the knowledge of the spectroscopic properties of the isomer are not sufficient to allow for the latter. The isomer decays to its ground-state via three decay channels: (i) internal conversion (IC), (ii) γ emission and (iii) bound internal conversion (BIC). The strength of the decay channels and thus the lifetime of the isomer depends strongly on its charge state. For neutral ^229mTh the dominant decay channel is IC. In this talk, lifetime measurements of the internal conversion decay channel are presented. A half-life of 7±1 μs has been measured for neutral ^229mTh which is well in agreement with theoretical predictions.