Plutonium contaminated soil particles

Cooper et al. (1994) have reported re-suspension studies on soils contaminated with plutonium during nuclear weapons tests by use of a mechanical dust-raising apparatus. Airborne dust was analysed in terms of mass and Am activities for particle sizes less than 7 pm. The AMAD was determined as 4.8-6 pm for re-suspended soil. Also, surface soil was characterised in the laboratory by means of sieving and microparticle classification, yielding mass and "Am activity distribution with respect to size. Data indicate the granularity of plutonium contamination at both major and minor trial sites. Depth profile analyses for undisturbed areas demonstrate that most (74% on average) of the americium and plutonium activity is found in the top 10 mm of soil. Plutonium and americium activities were found to be enhanced in the inhalable fraction over their values in the total soil, and the enhancement factors were similar in re-suspended dust and surface soil. Observed enhancement factors ranged from 3.7 to 32.5. 

Somewhat different results were found in studies from the British Atomic Weapons Test Site at Maralinga, South Australia, where specific activities were noted to be greater in the soil size fractions >90 pm (Ellis and Wall, 1982). Presumably there are numerous factors that might influence the relationship of plutonium activity with soil particle size including the nature of the contaminating event, the degree of weathering since the contamination event, the chemical nature of the soil, and the particle size distribution of the soil. 

Since soil-adsorbed plutonium contamination exists as discrete particles of various sizes, analysis of larger soil volumes (25 to 100 grams) is recommended (Bernhardt 1976). Commonly, soil samples with high amounts of carbonate are difficult to analyze. More rapid, efficient, and economical procedures are being developed to sequentially analyze a number of radioactive actinides (Flindman 1986). 

Radionuclide Exposure of the Embryo/Fetus (1998) Recommended Screening Limits for Contaminated Surface Soil and Review of Factors Relevant to Site-Specific Studies (1999) Biological Effects and Exposure Limits for Hot Particles (1999) Scientific Basis for Evaluating the Risks to Populations from Space Applications of Plutonium (2001)... 

Emitted by heavy atoms, such as uranium, radium, radon, and plutonium (to name a few), alpha particles are helium nuclei, making them the most massive kind of radiation. Alpha radiation can cause a great deal of damage to the living cells it encounters, but has such a short range in tissue (only a few microns) that external alpha radiation cannot penetrate the dead cells of the epidermis to irradiate the living cells beneath. If inhaled, swallowed, or introduced into open wounds, however, alpha radiation can be very damaging. In nature, alpha radiation is found in rocks and soils as part of the minerals, in air as radon gas, and dissolved in water as radium, uranium, or radon. Alpha emitters are also found in nuclear power plants, nuclear weapons, some luminous paints (radium may be used for this), smoke detectors, and some consumer products. Objects and patients exposed to alpha radiation may become contaminated, but they do not become radioactive. 

Some quantitative insight into the transfer through the soil may be obtained from the behavior of the fallout plutonium. This represents an analogy to an industrial contamination by high fired PuC particles of a grain size about 0.04 y. 

Atmospheric testing of nuclear weapons has been the main source of plutonium dispersed in the environment. Accidents and routine releases from weapons production facilities are the primary sources of localized contamination. Consumer and medical devices containing plutonium are sealed and are not likely to be environmental sources of plutonium (WHO 1983). Plutonium released to the atmosphere reaches the earth s surface through wet and dry deposition to the soil and surface water. Once in these media, plutonium can sorb to soil and sediment particles or bioaccumulate in terrestrial and aquatic food chains. 

Plutonium aerosols can be formed in various ways, including (a) oxidation or volatilisation of Pu metal, (b) oxidation or volatilisation of irradiated U or UO2, (c) droplet dispersion from aqueous solutions or suspensions of Pu, and (d) resuspension of soil or dust which has become contaminated with Pu. The particle size of Pu-aerosols is very variable, depending on the mode of formation. 

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