| Popis: |
Physico-chemical studies on environmental plutonium are described, which provide data integral to an assessment of dose for the inhalation of artificial actinides by Australian Aborigines living a semi-traditional lifestyle at Maralinga and Emu, sites of U.K. atomic weapons tests between 1953 and 1963. The most significant area, from a radiological perspective, is the area contaminated by plutonium in a series of “one point” safety trials in which large quantities of plutonium were dispersed explosively at a location known as Taranaki. Surface soil from the sites studied was characterized in the laboratory by means of sieving and microparticle classification, yielding mass and americium-241 activity distributions with respect to size. All soils are characterized as sandy, with the greatest mass generally associated with the 250–500 μm fraction. The amount of soil in the fraction centred on 5 μm (optical size) was generally in the range 0.5–1.0%. Thus, these soils are not considered particularly fine. The activity distribution of plutonium and americium with particle size is quite different from the mass distribution, as a considerably higher proportion of the activity is contained in the finer (inhalable) fraction than of the mass. Except in areas which were disturbed through ploughing during a cleanup in 1967, most of the activity remains in the top 1 cm of the surface. Much of the activity is in particulate form, even at distances > 20 km from the firing sites, and discrete particles have been located even at distances beyond 100 km. Data are presented which permit the assessment of annual committed doses through the inhalation pathway, for Aborigines living a semi-traditional lifestyle in the areas affected by the Taranaki firings in particular. Estimated doses at the boundary of the test range are presented, based on the new tissue weighting factors recommended by the International Commission on Radiation Protection (ICRP) and the new lung model recently adopted by ICRP. Some ideas are presented on rehabilitation of the area, defining those regions for which unrestricted land use is possible, and indicating a boundary within which contaminated soil will need to be removed, even for lower occupancy use such as transit and hunting. |
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