Gamma dose rate and soil gas radon concentration measured at low soil thickness (Czech Republic)

According to Czech legislative, the soil gas radon measurements are performed in a standard depth of 80 cm. However, on some localities characterized by low soil and subsoil thickness, this depth is not achievable. Therefore, the main aim of research activities was oriented to find out the depth relationship of soil gas radon concentration and its relation to additive radiometric parameters-gamma spectrometry and gamma dose rate. For practical use, the gamma dose rate was found to have better relationship to radon concentration than uranium concentration or total activity. The soil gas radon measurements were performed on 106 localities in the Czech Republic using the modified probe with side inlet of soil gas. The measurements were oriented to localities with demonstrably low thickness of soils and subsoils (in average 30-40 cm from surface to unweathered underlying rock). The choice of localities covered the most frequented rock types of the Czech Republic differing by radon index. For each locality, the complementary radiometric parameters (gamma dose rate and gamma spectrometry) were measured on the soil surface and closely situated rock outcrops. The growth of radon concentration with depth was confirmed on most of the localities with linear regression coefficient R = 0.95. The linear regression relationship was found between maximum soil gas radon concentration and gamma dose rate measured on the rock outcrops with coefficient R = 0.65 for all summarily processed data. The differences of this relationship were observed according to variability of lithological types and ranges of gamma dose rate. In a specified gamma dose rate ranges, the results could contribute to precising the method of building site assessment in conditions of low soil and subsoil thickness.