Presentation Rapid determination of Pu isotopes in soil and sediment samples by sector field inductively plasma mass spectrometry.

Zheng, Jian  ,  Wang, Zhongtang  ,  Ni, Youyi  ,  Men, Wu  ,  Tagami, Keiko  ,  Uchida, Shigeo

The globally distributed 239Pu (T1/2 = 2.4×104 years), 240Pu (T1/2 = 6.5×103 years) and 241Pu (T1/2 = 14.4 years) background resulted from nuclear weapon detonations in the last century. Meanwhile, regional Pu inputs are found at places adjacent to nuclear weapon test sites and nuclear accident sites. Since its introduction into the environment, attention has been given to studying Pu not only for the purpose of radiological assessment and preparedness for nuclear emergency due to its radiotoxicity, but also for applications using Pu as a tracer to study biological and geochemical processes, e.g. soil to plant transfer, soil erosion and sediment dating.In this study, a new chemical separation method was developed for rapid determination of Pu in soil and sediment samples, based on the following investigations: extraction behaviors of interfering elements (IEs, for ICPMS measurement) on TEVA resin; decontamination of U using TEVA, UTEVA and DGA resins and the impact of co-precipitation on Pu determination. The developed method consists of four steps: HNO3 leaching for Pu release; CaF2/LaF3 co-precipitation for the removal of major metals and U; the proposed TEVA+UTEVA+DGA procedure for the removal of U, Pb, Bi, Tl, Hg, Hf, Pt and Dy; and ICPMS measurement. The accuracy of this method in determining 239+240Pu activity and 239Pu/240Pu and 241Pu/239Pu atom ratios was validated by analyzing five standard reference materials (soil, fresh water sediment and ocean sediment). This method is characterized by its stable and high Pu recovery (90-97% for soil; 92-98% for sediment) and high decontamination factor of U (1.6 × 107) which is the highest reported for soil and sediment samples. In addition, the short analytical time of 12 h and the method detection limits, which are the lowest yet reported in literature, of of 0.56 μBq g-1 (0.24 fg g-1) for 239Pu, 1.2 μBq g-1 (0.14 fg g-1) for 240Pu, and 0.34 mBq g-1 (0.09 fg g-1) for 241Pu (calculated on the basis of a 1 g soil sample) allow the rapid determination of ultratrace level Pu in soil and sediment samples. The whole analytical method takes about 12 h (HNO3 leaching: 4h; filtration: 1 h; coprecipitation: 1h; Pu separation on extraction resin: 2 h; sample preparation for ICPMS measurements: 4 h) for 20 samples, which can be finished within two days. Compared to the method based on anion-exchange chromatography, which usually takes about 4-5 days for Pu separation, this method significantly shortens the analytical time. In addition, this method produces a small amount of hazardous waste acid and requires less evaporation of acid, greatly reducing the burden of radioactive laboratory management. This method has been applied to our study on soil-to-plant transfer of Pu, and analytical results of 239+240Pu activity and 240Pu/239Pu isotopic ratios in Japanese upland soils will be presented. Acknowledgements: This work was partially supported by the Agency for Natural Resources and Energy, the Ministry of Economy, trade and Industry (METI), Japan.

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