The new QST bioassay laboratory in Chiba, Japan

Japan's National Institutes for Quantum Science and Technology (QST) was designated as the core radiation emergency medical support center by the country's Nuclear Regulation Authority (NRA) in 2019. One of the main missions of the QST is to maintain and improve its dose assessment capability for radiation-exposed individuals. Toward the goal of effectively fulfilling this mission, a new facility-the Dose Assessment Building for Advanced Radiation Emergency Medicine-was constructed at the Chiba base of the QST in 2020. An integrated bioassay laboratory was installed in this facility for assessing subjects' internal doses, along with a new integrated in vivo counter. The bioassay capability of the new laboratory is currently expected to screen 5-10 persons simultaneously assuming internal contamination with actinides such as Pu, Am/Cm and U, although this is dependent on the specific contamination circumstances.

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

To provide timely information for prompting decision-making in emergency radiation therapy, we developed simple and rapid mass and alpha spectrometric methods for urinary bioassays to determine ultra-trace actinide isotopes. For the mass spectrometric method, after organic matter decomposition, LaF3/CaF2 co-precipitation and chromatographic purification using 2 ml of AG MP-1 M anion exchange resin, U and Pu isotopes were measured in a 20-ml urine sample by inductively coupled plasma-mass spectrometry. In the alpha spectrometric method, after organic matter decomposition, iron hydroxide co-precipitation and chromatographic purification using 2 ml of TEVA and 2 ml of DGA resin cartridges, Pu, U and Am/Cm isotopes were measured in a 500-ml urine sample by alpha spectrometry. These alpha and mass spectrometric methods were then applied for participation in the 2020 intercomparison organized by the Association for the PROmotion of Quality COntrol in RADiotoxicological Analysis (PROCORAD), France, for method validations.

Rapid analysis of 237Np and Pu isotopes in small volume urine by SF-ICP-MS and ICP-MS/MS

Internal contamination with alpha-particle emitting actinides, such as ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, is likely to bring a large amount of dose to the tissues of persons even if the intake amount is small. To provide timely information for prompt decision-making in radiation emergency therapy, we developed a simple and rapid method for urinary bioassay to determine ultra-trace ²³⁷Np and Pu isotopes using SF-ICP-MS and ICP-MS/MS. To avoid polyatomic interferences and tailing effects from U, ²³⁷Np and Pu isotopes were collected after removing U effectively using a simple single chromatographic column packed with 2 mL AG MP-1M anion exchange resin, exhibiting a high decontamination factor of 10⁸ for ²³⁸U. The overall chemical fractionation between ²³⁷Np and ²⁴²Pu for the whole analytical procedure was 0.974 ± 0.064 (k = 2), allowing us to measure ²³⁷Np and Pu isotopes using ²⁴²Pu as a yield tracer with yields of 76 ± 5%. Using ICP-MS/MS with low background provided the method detection limits for ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu of 0.025, 0.025, 0.015, and 0.020 fg mL^-1, respectively, for 20 mL of urine sample. Those were comparable to detection limits of SF-ICP-MS with high sensitivity. Subsequently, three urine reference materials with Pu spike, provided by the Association for the PROmotion of Quality COntrol in RADiotoxicological Analysis (PROCORAD), France, were analyzed by the developed method and the conventional alpha spectrometry technique for validation. Finally, the developed method was successfully employed to measure the contamination level of ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu in urine samples collected during decorporation therapy using DTPA, after a Pu inhalation exposure accident in Japan. The high throughput (9 h for 12 samples), simplicity, low cost, and high sensitivity of the method will allow greater numbers of related laboratories to be involved in screening activities for unexpected actinide exposure, such as in the case of a large scale radiological disaster.