Methods for isolating plutonium particles in Maralainga soils

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Australian Nuclear Science and Technology Organisation
A combination of density-separation and gamma testing methods was used to isolate a plutonium (Pu)-containing particle from the host Maralinga soils. Such separation is necessary in order to reduce or eliminate interference from other elements in the host soils that may occur during analysis methods (e.g., synchrotron XANES) used for determining physico-chemical information such as compound speciation and oxidation state. Soil samples were obtained from the Taranaki test area, at Maralinga, South Australia, where Pu had been dispersed by high explosive detonation and through burning in the 1950s. Bulk soil samples were first screened using HPGe gamma-ray spectrometer for detection of Am-241 (0.060 MeV gamma emission) which co-exists with the Pu in the dispersed particles at a concentration ratio of approximately 1:7.5 (Am-241 to Pu-239). The sample was sieved (125 μm) to remove large sand particles and debris. Density separation was accomplished by repeated sonification (0.5 in. probe tip sonifier) and centrifugation of mixtures of soil and lithium heteropolytungstate (density of 2.9 g/ml). The various density fractions were tested for Am-241 through gamma counting. This process was repeated until a small mass (<0.01 g) of heavy particles remained. Further isolation was accomplished using microscope, physical separation, and gamma counting. The result of the process was isolation of a small particle, containing Am and Pu isotopes that had been originally part of a non-critical nuclear weapons test. The particle had been dispersed approximately two kilometres through the air pathway, and has been subjected to +60 years of weathering and chemical interaction processes. The isolation process allows for further testing of the Pu, without interference from natural soil elements, to provide a range of pathway, biological uptake, and dose information.
Plutonium, Particles, Soils, Nuclear test sites, Valence, Sampling, South Australia, Australia, Fission products, Lithium
Mokhber-Shahin, L., Johansen, M. P., Collins, R. N., & Payne, T. E. (2012). Methods for isolating plutonium particles in Maralinga soils. Paper presented to the 12th South Pacific Environmental Radioactivity Association Conference (SPERA 2012), Sydney, Australia, Tuesday 16 October – Friday 19 October 2012. Lucas Heights, NSW: Australian Nuclear Science and Technology Organisation, (pp. 59).