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The prevailing radon risk in particular rock type is characterised by four radon risk categories. The distribution in three main categories (low, medium and high) is made by the comparison of radon concentration and the soil gas permeability. The intermediate category of radon risk is intended for inhomogeneous Quaternary sediments. We have used the soil gas radon database of Czech Geological Survey and the database of indoor radon measurements of State Office for Nuclear Safety to examine the effect of the geological bedrock on the resulting mean soil gas radon concentration and indoor radon concentration on the Quaternary sediments.
After the ArcGis projection of the databases to vectorised contours of geological units, we have counted the mean values of soil gas and indoor concentrations according to the radon risk category of the geological bedrock of the Quaternary sediments. The first statistical results show high effect of the bedrock on the level of soil gas radon concentrations and indoor radon concentrations measured on the Quaternary sediments. The mean values of soil gas radon concentrations measured on the Quaternary sediments with high radon index bedrock are 2,4 times higher in comparison with the measurements made on the places with low radon index of the bedrock, resp. 1,8 x higher compared to the values measured on medium risk; when the mean soil gas radon concentration on the bedrock with high radon index is 52 kBq.m-3, 30 kBq.m-3 on the medium radon index and 22 kBq.m-3 on the low radon index. Indoor radon concentrations measured on the bedrock with the high radon index are 2,7 higher compared to the measurements made on the bedrock with low radon index and 2 times higher in comparison with the bedrock with low radon index. The mean indoor radon concentrations measured on the bedrock with high, medium or low radon index are 440, 220 and 160 Bq.m-3. Both high soil gas and indoor radon concentrations are to be expected on the places where the bedrock of Quaternary sediments is formed by the geological units with medium and high radon risk index.
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