Characterization of Pu concentration and its isotopic composition in a reference fallout material Original Research Article

Because there is no reference material for fallout plutonium isotope monitoring, preparation of such a material is necessary for quality control of fallout radionuclides analysis for atmospheric environmental studies. In this work, we report the characterization of Pu activity and its isotopic composition in a reference fallout material prepared by the Meteorological Research Institute (MRI), Japan. This material was prepared from samples collected at 14 stations throughout Japan in 1963–1979, with reference values of 137Cs, 90Sr and 239 + 240Pu activities. We analyzed the activities of 239 + 240Pu and 241Pu, and the atom ratios of 240Pu/239Pu and 241Pu/239Pu using an isotope dilution sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS). The 239 + 240Pu activities in this fallout material using acid leaching and total digestion were 6.56 ± 0.20 mBq/g and 6.79 ± 0.16 mBq/g, respectively. Atom ratios of 240Pu/239Pu were 0.1915 ± 0.0030 and 0.1922 ± 0.0044, respectively. Both 240Pu/239Pu and 241Pu/239Pu atom ratios were slightly higher than those of global fallout, which could be attributed to the deposition of fallout radionuclides resulting from the Chinese nuclear weapons tests conducted in the 1970s. The dominant host phases of 239 + 240Pu were found to be organic matter-sulfides (70%) with a relative high 240Pu/239Pu atom ratio, and Fe–Mn oxides (19%) using a sequential extraction method.