The uncertainty in gamma spectroscopic activity measurements is investigated for soil containing hot particles. A radioactivity inhomogeneity uncertainty needs to be taken into account, which depends on the density of hot particles in the sample geometry, the distribution of their activities, and the specific source-detector geometry. The maximum activity error due to hot particles in our sampled Chernobyl soil with a 137Cs activity of 100 kBq kg(-1) soil was 6% for our source detector geometry. The methodology presented might have a practical application in nuclear power plants to detect hot particles in a large quantity of dust or dirt. The number of hot particles present can be estimated if the activity of all particles is assumed to be similar. With this assumption 100 g of the investigated soil sample would contain about 500 hot particles with an approximate activity of 20 Bq each.

The Chernobyl accident in 1986 resulted in the widespread identification of the post-accident presence of radioactive (or ‘hot’) particles across large areas of Eastern and Central Europe. Such particles arise from direct deposition and also from condensation and interactions on particle surfaces during and following the deposition of soluble fallout. Identification of the presence and nature of hot particles is necessary in order to determine the long-term ecological impact of radioactive fallout. This paper describes several techniques for the identification and characterization of hot particles in soil samples from Belarus. In addition to new results from the use of gamma spectrometry, we include two novel instrumentation approaches that have been developed and applied to Chernobyl fallout-contaminated soils. The first, ‘differential’ autoradiography, utilizes a photographic film sandwich to characterize the nature of the ionizing radiation emitted from samples. In this paper we show that differential autoradiography can not only identify hot particle presence in soil, but can also determine the dominant radionuclide in that particle. The second approach, sector field ICP-MS (ICP-SFMS), can provide rapid, high-precision determination of the actinides, including the transuranic actinides, that characteristically occur in hot particles originating from weapons fallout or fuel matrices. Here, ICP-SFMS is shown to yield sufficiently low detection limits for plutonium isotopes (with the exception of 238Pu) to enable us to confirm negligible presence of plutonium in areas outside the Chernobyl exclusion zone, but with high levels of fission-product contamination.

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A new method is presented to interpret data on diffusion-sorption processes obtained from through-diffusion experiments. Both sorption and desorption are modeled as kinetically controlled processes by incorporating nonlinear isotherms. The diffusion-sorption equation was solved numerically and the resulting algorithm was integrated into a nonlinear regression code to test various models. The through-diffusion technique was modified such as to obtain sorption and desorption data from a single experiment. Data are presented for the diffusion of cesium through a Eutric Cambisol soil pellet. Various sorption models were tested. The best fit to the experimental data was obtained assuming first-order kinetics with a Freundlich isotherm. Desorption shows a marked hysteresis.

The development of hot particles was observed in a pure quartz sand as well as in "Ea" horizon material from a humo ferric podzol after ionic contamination with radiocesium. Therefore, fallout that contaminates soil with radiocesium in an ionic form can lead to the formation of hot particles for which health impact must be assessed differently compared to homogeneously contaminated soil.