Analytical method for the determination of Np and Pu in sea water by AMS with respect to the Fukushima accident

Abstract

A chemical separation procedure for plutonium (Pu) and neptunium (Np) was developed using extraction chromatography, mass spectrometry and radiometric analysis to determine their concentrations and isotopic ratios in sea water. 241Am, which causes isobaric background to 241Pu in mass spectrometric measurements, was successfully separated from the Pu fraction by this method. Water samples which were spiked with 242Pu and 237Np or 239Np, respectively, were used for chemical yield determination. The chemical yields of Pu and Np, which were determined by alpha and gamma spectrometry at the Radiochemie München (RCM), of more than 85% were obtained. The developed method was applied to analyze the concentration of Pu and Np in the certified reference material, IAEA-443, by Accelerator Mass Spectrometry (AMS) at the Maier–Leibnitz-Laboratory (MLL) to check the applicability of the method to sea water samples. The concentrations of 240Pu, 241Pu and 237Np obtained in this study are in agreement with the certified and literature values within the uncertainties. Due to strong isotopic interference of 239Pu with 238U, it was not possible to analyze the concentration of 239Pu. Some modifications of the chemical separation method to suppress the uranium (U) fraction are under consideration. This method can be used for the analysis of Pu and Np in Pacific Ocean water samples collected after the Fukushima accident.