Rapid measurement of actinides in urine by mass and alpha spectrometric methods

In 2017, five workers were involved in the internal contamination accident at a nuclear facility of the Japan Atomic Energy Agency in Oarai-town, Ibaraki Prefecture, Japan. They accidentally inhaled plutonium compounds (containing Pu and Am isotopes) and the maximum committed effective dose was estimated as a range of 100−200 mSv [1]. Internal contamination with alpha-particle emitting actinides, such as 239Pu, 240Pu, is likely to bring a large amount of dose to the tissues of persons even if the intake amount is small. Therefore, after this accident, medical intervention using decorporation agents (Ca/Zn-DTPA) to patients was performed for the first time in Japan. This chelation therapy was continued for several weeks or months and ca. 200 urinary samples were collected from the five workers before and after each DTPA administration. To cope with similar situations in the future and provide timely information for prompt decision-making in radiation emergency therapy, we are attempting both the optimization of a conventional method based on alpha spectrometry and the development of a screening method based on mass spectrometry [2]. In terms of mass spectrometric method, to eliminate matrix, polyatomic interferences and tailing effects from U, after LaF 3 /CaF 3 coprecipitation, Pu isotopes were collected after removing U effectively (exhibiting a high decontamination factor of 108 for 238U) using a single chromatographic column packed with 2 mL AG MP-1M anion exchange resin. The Pu isotopes were measured using 242 Pu as a yield tracer with yields of 76±5%. Using ICP-MS/MS with low background, very low method detection limits for 239 Pu, 240 Pu, and 241 Pu of 0.057, 0.126, and 76.8 mBq L -1 , respectively, were obtained for 20 mL of urine sample. These detection limits were comparable to those of SF-ICP-MS with higher sensitivity [2]. In terms of alpha spectrometric method, after decomposing organic matter completely with HNO3 and H2O2 , in order to eliminate matrix and interferences, the combination of the iron hydroxide co-precipitation and the automated separation using the TEVA and DGA resin cartridges was used prior to 48 h counting using alpha spectrometer. This method presented stable and high (~ 80%) yields for Pu, Am, and U, and low method detection limits (< 0.5 mBq using 500 mL urine sample). Subsequently, these alpha and mass spectrometric methods were applied to participate in the intercomparison organized by the Association for the PROmotion of Quality COntrol in RADiotoxicological Analysis (PROCORAD), France, for method validation.
International Conference on Individual Monitoring of Ionising Radiation (IM2022) and Neutron and Ion Dosimetry Symposium (NEUDOS-14)