Lifetime Measurement of the super(229) Th <SCRIPT Nuclear Isomer

The first excited isomeric state of super(229) Th 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, [gamma] decay, and bound internal conversion), whose strengths depend on the charge state of super(229)mTh. We report on the measurement of the internal-conversion decay half-life of neutral super(229)mTh. A half-life of 7+ or -1[mu]s has been measured, which is in the range of theoretical predictions and, based on the theoretically expected lifetime of [approximate]10 super(4)s of the photonic decay channel, gives further support for an internal conversion coefficient of [approximate]10 super(9), thus constraining the strength of a radiative branch in the presence of internal conversion.