Preparation of 93Mo solution using proton irradiated Nb

Determination of 93Mo in Radioactive Samples of Sulfuric Acid Media from Nuclear Facilities

⁹³Mo is an important radionuclide in view of radioactive waste repository because of its long half-life and high mobility in the environment. ⁹³Mo decays by electron capture without any measurable gamma ray emission. The concentration of ⁹³Mo in most of the radioactive waste is many orders of magnitude lower than the major activation product radionuclides, which makes the accurate determination of ⁹³Mo a big challenge. A new analytical method for the determination of ⁹³Mo in sulfuric acid media from nuclear power reactor was developed. ⁹³Mo was separated from most of the radionuclides by cation exchange chromatography followed by the removal of sulfate by CaSO₄ precipitation. A further purification of ⁹³Mo, especially from anion species of ⁵¹Cr and ¹²⁵Sb, was achieved by anion exchange chromatography and a short alumina column separation. The chemical yield of ⁹³Mo in the entire separation procedure reached about 75%, and the decontamination factors for all potential interfering radionuclides were 1.5 × 10⁶-1.6 × 10⁸. The purified ⁹³Mo was measured by liquid scintillation counting through counting its low-energy Auger electrons. A detection limit of 2 mBq/g for ⁹³Mo in 50 g sample was achieved by this method, which enables the quantitative determination of ⁹³Mo in most of the radioactive samples in the decommissioning waste and coolant water of nuclear power reactors. The developed method has been successfully applied to determine ⁹³Mo in coolant water of nuclear power reactors, providing a robust analytical approach of ⁹³Mo for the radiological characterization of radioactive wastes.

First direct determination of the 93Mo half-life

This work presents the first direct measurement of the ⁹³Mo half-life. The measurement is a combination of high-resolution mass spectrometry for the determination of the ⁹³Mo concentration and liquid scintillation counting for determining the specific activity. A ⁹³Mo sample of high purity was obtained from proton irradiated niobium by chemical separation of molybdenum with a decontamination factor larger than 1.6 × 10¹⁴ with respect to Nb. The half-life of ⁹³Mo 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 ⁹³Mo decays to the metastable state ^93mNb 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 ⁹³Mo 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.