engleski

Dose Rate Conversion Factors, Soil Thickness and their Influence on Natural Background Dose Rate in Air Above Carbonate Terrains

The natural background dose rate in air above ground surface is the sum of doses arising from cosmic radiation and radionuclides in air, soil and bedrock. The resulting dose rate arising from radionuclides in soil and bedrock (ground component) is the product of characteristic radionuclides specific activity in soil or bedrock with the accompanying dose rate conversion factors (DRCF). The sum of products between unit dose rates from each emitted photon energy and the emission intensity of all accompanying radionuclides is presented with DRCF for characteristic radionuclide. DRCF are calculated for unit 40-K activity in soil and bedrock, as well as for unit head radionuclides activity of 232-Th decay series, 235-U decay series, 238-U - 230-Th subseries and 226-Ra - 210-Pb subseriesm, in relation to soik thickness. Presented DRFC values are generally in good agreement with those published previously, and strongly depend on soil thickness. Recalculation of ground component of natural background dose rate data collected by airborne or carborne surveys above carbonate terrains into radionuclides concentrations in the ground is possible in two cases. Recalculated values present radionuclide concentrations in bedrock in the case where soil has been completely missing. In the case of well-developed soil (thickness of 25 cm or more) it represents concentrations in soil relatively well. The laboratory gamma-spectrometry of 40-K, 226-Ra, 228-Ac or 208-Tl and 238-U in samples collected during conventional geochemicaal sampling provides a good database of characteristic radionuclides. Such a database is applicable for assessment of ground componrnts of natural background dose rate, as well as for geochemical map constructions.

dose rate; carbonate terrains; soil thickness; conversion factors

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