Studies on Speciation of Environmental Plutonium

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To improve impact assessments of radionuclide contamjnation in terrestrial ecosystem, informationon radionuclide species is essential.Deposited radionuclides in soil may be present in different physico-chemical forms, ranging from mobile low molecular mass ionic species to inert high molecular mass colloidal forms or particles.In this work, an attempt was made to characterize Pu in soil.For this purpose, highly contaminated soil samples by close-in fallout from atomic weapons tests at the former Soviet Union's Semipalatinsk nuclear test site were collected from Dolon settlements. This settlement was heavily exposed by the close-in fallout from the first nuclear test on 29 August 1949.The soil samples from Dolon settlement have been first measured for γ-emitting radionuclides(^<137>Cs and natural radionuclides).After that, Pu was determined, in which we employed the stepwise leaching method to get information on the geochemical association of Pu with soil.The inventories of 137Cs and 239,240Pu were in the wide range of 790-10,310 and 530-14,320 Bq/m^2, respectively.Sequential leaching of Pu from the soil showed that more than ca.80% of the ^<239,240>Pu found were not leached by hot digestion with conc. HNO_3 +H_2O_2, indicating the presence of Pu associated with fused silicates originating from local fallout debris. Furthermore, the presence of hot-particles from the Pu contaminants by α-track radiography technique using CR-39 polycarbonate was confirmed in the soil, even at present after about 50 years from the first nuclear weapon testing.