The risk of radon emissions is high in Estonia, especially in the northern part of the country where graptolite argillite (Dictyonema shale) crops out close to the ground surface. The behaviour and concentration of Rn in soil air vary considerably due to several reasons. To elucidate these, investigations were carried out in densely populated Harju County where the concentration of Rn is generally high and the risk to human health is the greatest. The investigations of soil air and in soil samples from the bottom of the excavations were carried out in 31 points. The assessments were made on the results of two simultaneously applied methods: calculated from eU concentration in soil measured with a gamma ray spectrometer, and by direct measurements in soil air with a Markus-10 emanometer. The results obtained by the two methods can notably differ.
In the high and very high Rn risk areas the concentration of Rn in the indoor air of dwellings was high as well. The main source of Rn there is the soil underneath the dwellings and/or bedrock, primarily radioactive graptolite argillite lying below the Quaternary deposits. Areas of such high Rn concentrations in the ground did not follow the genetic–lithologic types of Quaternary deposits. In the high Rn-risk areas within the klint zone the content of U, F, Mo, and some other elements exceeded the recommended and even permissible level for residential areas in several investigation points.
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