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内容記述 |
Various actinides are produced via neutron capture reactions involving uranium in burning uranium fuel in a nuclear reactor. Actinides are highly chemically toxic and have biologically dangerous α-rays. The value of the radiation weighting factor is larger for the types of radiation having larger effects on the human body (α-particles, 20; β-particles and γ-rays, 1). Many actinides that emit α-rays have a long physical half-life, and can exist in various valence states of III to VI. In the case of a nuclear accident, the actinides that had been produced during the normal operation of the reactor could be released into the environment, causing radioactive contamination and posing a radiation risk to humans. In addition, 237Np, 239Pu and 240Pu are also regarded as key long-term dose contributors in certain nuclear waste repositories. Therefore, it is important to study their concentration level, distribution, existence state, environmental behavior and radiation effects. Mass spectrometry, especially ICP-MS, as an atom-counting approach that counts the atoms themselves, irrespective of their decay mode, specific activity, or half-life, is gradually replacing/has replaced conventional radiometric methods, such alpha spectrometry, LSC etc. as a main-stream technique for hard-to-detect actinides analysis. Due to the strength of argon plasma source of ICP-MS, extremely high, almost 100% ionization efficiency can be achieved for actinides, thus, highly sensitive determination of actinides can be realized. For example, our recent development of sector-field ICP-MS (SF-ICP-MS) techniques has pushed the detection limit for analysis of actinides down to attogram levels [1]. To improve the sensitivity of ICP-MS for ultra-trace radionuclide analysis, two approaches can be considered. First, is the improvement of the sample introduction efficiency of ICP-MS by the hyphenation of a membrane desolvation system to ICP-MS. It has proved to be effective for enhancing actinides analysis sensitivity by a factor of 5 to 10 and lowering the formation of H2O-origin background species, such as oxides and hydrides (MO+ and MH+). Second is the use of larger sample sizes up to several tens of grams to increase the concentration factor of the target radionuclides in low-level environmental samples. With the increase of sample size, however, reducing the enhanced sample matrix effect is a great challenge for the SF-ICP-MS-based method development, which requires a powerful chemical separation capability. This lecture will discuss the determination of hard-to-detect actinides, Pu isotopes (239Pu, 240Pu, 241Pu), 241Am and 237Np using SF-ICP-MS in different environmental samples, such as soil/sediment, seawater, plants and radioactive Cs particles [2-6]. Chemical separation/purification methods for removal sample matrix (for example, separation of alkali and alkaline earth elements and REEs for ultra-trace 241Am analysis), separation of interfering elements to reduce/eliminate polyatomic and isobaric interferences (for instance, separation of U, Bi, Pb, Tl, Hg, Hf, Pt, Dy for actinides analysis), will be highlighted. Several radioecological application studies on Fukushima accident derived contamination impact of Pu in the environment [7], transfer of Pu from soil to rice [8], and monitoring 237Np activity concentration in seawater before and after the authorized release of contaminated water from Fukushima Daiichi Nuclear Power Plant will be presented. References[1]J. Zheng, J. Nucl. Radiochem. Sci. 15(1) 7-13 (2015).[2]Z. T. Wang, J. Zheng, Y. Ni, W. Men, K. Tagami, S. Uchida, Anal. Chem. 89, 2221-2226 (2017).[3]Z. T. Wang, J. Zheng, L. G. Cao, K. Tagami, S. Uchida, Anal. Chem. 88, 7387-7394 (2016).[4]J. Igarashi, K. Ninomiya, J. Zheng, Z. Zhang, M. Fukuda, T. Aono, H. Minowa, H. Yoshikawa, K. Sueki, Y. Satou, A. Shinohara, Environ. Sci. Technol. 58, 14823-14830 (2024). [5] S. Zhang, Z. Liu, G. Yang, J. Zheng, S. Pan, T. Aono, A. Sakaguchi, Anal. Chem. 95, 16892-16901 (2023).[6] X. Gu, B. Yang, G. Yang, M. Yamada, F. Wu, J. Zheng, Microchem. J. 208, 112480 (2025).[7] J. Zheng, K. Tagami, S. Uchida, Environ. Sci. Technol. 47, 9584-9595 (2013).[8] Y. Y. Ni, J. Zheng, Q. J. Guo, Z. Y. Huang, H. Wang, K. Tagami, S. Uchida, Catena, 210, 105884 (2022). |
