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A Development of the Quantitative Analysis Method for Np in Solutions by Various Radiometric Methods and Absorption Spectroscopy
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Neptunium (Np) is one of the daughter elements included in the decay chain of Pu. The quantitative analysis of Np isotopes is required for radioactive waste characterization, research on actinide chemistry, etc. Np-237 has a long half-life (2.144 million years), but its daughter Pa-233 has a relatively short half-life (26.975 days). For this reason, after a sufficient time elapses following the chemical preparation process of the analyte, the two nuclides are in radiation equilibrium in the sample. Np-237 emits alpha-rays while Pa-233 emits beta-rays. Both nuclides also emit gamma- and X-rays. In this study, alpha-rays were measured using liquid scintillation counting (LSC) method and alpha spectrometry. Gamma-spectrometry with a HPGe detector was used for the analysis of gammaand X-rays. In addition, we compared the radiometric results with quantitative analysis of Np using UV-Vis absorption spectrometry. The LSC method and the HPGe gamma-spectroscopy do not require extensive sample preparation procedures. Alpha spectroscopy requires a standard material spiking, separation by coprecipitation, and disk-type sample preparation procedure to obtain measurement efficiency and recovery factor. A reference material sample with a concentration of 5.8 mM was analyzed by the four analysis methods, and all of the measured results agreed well within a difference level of 4%.
