Uranium Concentration Analysis By Visible Absorption Spectroscopy- Temperature and Solution Matrix Control

Mo-99 (66 h half-life) decays to Tc-99m, the dominant medical isotope used in nuclear medicine. The Office of Material Management and Minimization (M3) within the National Nuclear Security Administration (NNSA) has an objective to â??accelerate the establishment of a reliable, commercial Mo-99 supply network that avoids a single point of failure and does not use proliferation-sensitive HEU (High Enriched Uranium)â??. This remit includes a cooperative agreement with SHINE medical technologies, a company aiming to produce Mo-99 domestically in the US. SHINE plans to use a deuterium-tritium neutron generator to produce fission Mo-99 from Low Enriched Uranium (LEU) sulfate solutions. Therefore, the determination of uranium concentration in uranium sulfate solutions is an important consideration for SHINE. Utilizing the Beer-Lambert Law allows for uranium concentration analysis using the characteristic visible absorption spectra of the uranyl cation dissolved in 1 mol/L sulfuric acid. The molar absorptivity (ε) at λmax was calculated previously using accurate standard solutions, with different UV-vis cells tested, impurities screened and data collection methods refined. However, comparison with the Davis-Gray uranium analysis technique revealed the importance of temperature control for accurate and precise measurement, with ε varying significantly as a function of temperature. To address this issue a newly installed Peltier unit was used to control cell temperature and ε determined from freshly prepared standard solutions over a range of uranium concentrations at a fixed temperature. To test the accuracy and precision of the refined technique, the concentration of uranium of 10 unknown samples were then measured at the same temperature. Finally, the impact of temperature on ε was analyzed for uranium, not just in 1 mol/L sulfuric acid but also 1 mol/L nitric and hydrochloric acids, thus facilitating an evaluation of technique general applicability.