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内容記述 |
237Np, owing to its long half-life (t1/2=2.14×106 y) and similar conservatism to 137Cs, has the potential to replace 137Cs for water mass circulation studies on decades and even longer time scales. Due to its high mobility in the environment, monitoring 237Np activity concentration level is important for radiation protection study. A new method for the determination of 137Cs, 237Np, and Pu isotopes in seawater and freshwater samples was proposed to solve the difficulty of 237Np quantitative analysis. The developed method includes the separation technique of ammonium phosphomolybdate (AMP) adsorption for 137Cs and anion exchange chromatography for 237Np and Pu, measurement technique of gamma spectrometry for 137Cs and SF-ICP-MS for 237Np and Pu isotopes. 242Pu as a pseudo isotope dilution tracer for 237Np, the negligible chemical fractionation between 237Np and 242Pu of 1.02 0.06 (k=2) was obtained by implementing sophisticated control of the redox system and chromatographic elution optimization. The analytical results for IAEA-443 Certified Reference Materials agreed with the reference values, showing chemical yields of 65−88%, U decontamination factor above 106 level, and improved sample throughput (5 days for 12 samples). Meanwhile, the lower method detection limits (MDLs) of 237Np, 239Pu, and 240Pu were 1.310-3, 0.065, and 0.15 μBq L-1 for 15 L water sample, respectively. This confirms that our method can efficiently analyze ultra-trace 237Np and Pu isotopes in seawater and freshwater samples. In addition, the 237Np activity concentrations of 0.122−0.156 μBq L-1 in the Pacific Ocean seawater around the FDNPS were reported for the first time. This new rapid analytical method developed in this study improved the analytical capabilities of ultra-trace 237Np and Pu isotopes and was used for monitoring seawater following the authorized release of contaminated water from the FDNPS to the ocean to evaluate the potential radiological impact on the marine ecosystem. It was also employed for the investigation on activity concentration level of 237Np and Pu isotopes in freshwater samples. Results on the activity concentration level of 237Pu and Pu isotopes in seawater and in freshwater (river and tap water) and their contamination sources will be discussed. |
