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The relationship of soil gas radon Rn 222 and indoor radon was studied within the Quaternary fluvial sediments of the Czech Republic. The processing of data selection from the radon database of the Czech Geological Survey and indoor radon data (database of the National Radiation Protection institute) has proved the concentration dependence of radon in Quaternary fluvial sediments on deeper bedrock. The ArcGIS processing was accompanied by the field verification in five profiles, intersecting the granitoid Central Bohemian Plutonic Complex and its rim rock types. Both theoretical and experimental results show dependence of soil gas radon and indoor radon concentrations in Quaternary fluvial sediments on deeper geological basement, thus leading to the conclusion that the lateral transport of Quaternary sediments does not play such a dominant role in radon concentrations, as was thought previously. This fact will enable to determine precisely the radon index of Quaternary sediments (in the Czech radon mapping classified as an intermediate index) into three categories according to the lithology of their geological basement.

A comparison of Czech indoor radon data, soil gas radon data and gamma dose rate was performed on the data sets of 92,276 indoor radon measurements in existing dwellings (National Radiation Protection Institute - NRPI), database of 9500 test sites of soil gas radon measurements (Czech Geological Survey - CGS) georeferenced to levels of gamma dose rate map. Three methods were used for the study of soil gas Rn-indoor Rn relationship: (1) based on the vectorised point soil gas and indoor data related to vectorised areas of gammadose rate, (2) vectorised soil gas-indoor data based on vectorised geological units and (3) soil gas and indoor data related to grid squares 10 x 10 km2. The first and second methods seem to express the closer correlation compared with the third one, however the correlation using the third method is influenced by the representativeness of data value in the square of 100 km2 area. On the other hand, the third method can be used for the overview coverage of the continental areas with lack of input information.