Characterization of typical transuranic nuclides in a reference fallout material using SF-ICP-MS

For the quality control in determining transuranic nuclides in fallout samples, this work first reported the ²³⁷Np activity concentration in a reference fallout material and further calculated the activity ratios of ²³⁷Np/^239+240Pu and ²³⁷Np/²⁴¹Am, and the atom ratio of ²³⁷Np/²³⁹Pu in it. The reference fallout material prepared by the Meteorological Research Institute was collected at 14 stations throughout Japan in 1963-1979. The ²³⁷Np and Pu isotopes (²³⁹Pu and ²⁴⁰Pu) were separated and purified using AG MP-1M anion-exchange resin, quantified using ²⁴²Pu as an isotope dilution tracer, and determined by the SF-ICP-MS. The analytical method was validated by the analysis of 4 sediment reference materials. The activity concentrations of ²³⁷Np, ²³⁹Pu and ²⁴⁰Pu were (25.9 ± 0.6) × 10^-3, 4.10 ± 0.01 and 2.89 ± 0.04 Bq/kg, respectively, in the investigated reference fallout material. The activity ratio of ²³⁷Np/^239+240Pu (3.7 ± 0.1) × 10^-3 was consistent with the global fallout evaluation value. The ²³⁷Np/²³⁹Pu atom ratio of 0.561 ± 0.014 was higher than the average global fallout value of 0.41 ± 0.010, indicating the necessity of establishing regional characteristic global fallout value of ²³⁷Np/²³⁹Pu atom ratio for assessment of radioactive contamination. Comparison of the ²³⁷Np/^239+240Pu activity ratios between in the reference fallout material and in soils over several decades indicated that ²³⁷Np has stronger migration capability than Pu isotopes in soils because ²³⁷Np was depleted compared to reference fallout material.