First direct determination of the Mo half-life.

This work presents the first direct measurement of the Mo half-life. The measurement is a combination of high-resolution mass spectrometry for the determination of the Mo concentration and liquid scintillation counting for determining the specific activity. A Mo sample of high purity was obtained from proton irradiated niobium by chemical separation of molybdenum with a decontamination factor larger than 1.6 × 10 with respect to Nb. The half-life of Mo was deduced to be 4839(63) years, which is more than 20% longer than the currently adopted value, whereas the relative uncertainty could be reduced by a factor of 15. The probability that the Mo decays to the metastable state Nb was determined to be 95.7(16)%. This value is a factor of 8 more precise than previous estimations. Due to the man-made production of Mo in nuclear facilities, the result leads to significantly increased precision for modelling the low-level nuclear waste composition. The presented work demonstrates the importance of chemical separations in combination with state-of-the-art analysis techniques, which are inevitable for precise and accurate determinations of nuclear decay data.