Development of a new bioassay laboratory at QST

The national system for radiation emergency medicine in Japan was revised based on the lessons learned from the Fukushima Daiichi Nuclear Power Plant accident. This system was further revised in 2019; specifically, the Nuclear Regulation Authority of Japan designated the National Institutes for Quantum Science and Technology (QST) as the national core center for coordinating and guiding four other Advanced Radiation Emergency Medical Support Centers. These centers will be responsible for providing medical treatments of severely exposed or contaminated patients as well as maintaining human resources to respond to nuclear disaster through a wide variety of training courses. Diagnostic dose assessment for patients is also one of the important missions of the centers.To enhance the capability for dose assessment of patients internally contaminated with actinides, the QST started operation of a new facility named the Dose Assessment Building for Advanced Radiation Emergency Medicine. A new bioassay laboratory was installed at this facility as well as an integrated in-vivo counter (Tamakuma et al., this issue). This laboratory has two rooms for pretreatment of excreta samples equipped with ashing, digestion and purification devices, and one analytical room with various measurement devices.Our current main interest is to establish a rapid and labor-saving bioassay method for actinides that are likely to cause significant internal exposure. In 2017, five workers from a Japanese nuclear facility accidentally inhaled plutonium compounds; this accident was the first Japanese case associated with medical intervention using decorporation agents (Ca/Zn-DTPA) [1]. QST was involved in the medical treatment and dose assessment, and our bioassay laboratory presented the 239+240Pu and 241Am data by collecting and analyzing ca. 200 urinary samples. To cope with similar situations in the future, 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. It is possible to measure U, Pu and Am isotopes by alpha spectrometry; however, mass spectrometry offers a more feasible, less time-consuming method to measure these long-lived actinide isotopes with low specific activity. The combined use of two mass spectrometry devices (SF-ICP-MS and ICP-MS/MS) allows us to rapidly measure multiple actinides (e.g., 234U, 235U, 238U, 237Np, 239Pu, 240Pu) in small-volume urine samples (e.g., 20 ml) and to present the isotope ratios (e.g., 240Pu/239 Pu) for source identification [2]. For fecal samples, microwave-assisted aging and digestion are used to shorten the pretreatment to < 8 h. Our developed techniques have been tested and validated through relevant exercises (e.g., PROCORAD) for the purpose of obtaining future international accreditation.International Conference on Individual Monitoring of Ionising Radiation (IM2022) and Neutron and Ion Dosimetry Symposium (NEUDOS-14