Soil radon levels measured with SSNTD's and the soil, radium content

The source of the radon gas 222Rn in the ground air is the soil and the bedrock underneath. The potential radon level in the ground is given by the content of 226Ra in the ground. The presence of 226Ra is in turn dependent on the amount of 238U in the ground, and these two isotopes are not always found to be in equilibrium in a sample of soil or bedrock. Especially if the soil is washed out, the radium content may be reduced. When the soil is the relevant source of the radon gas, it is interesting to look for a possible relation between the radon level and the radium content of the soil. In this paper we report on measurements of soil radon levels carried out with SSNTDs at several European sites. Soil samples were collected at these sites and analysed with gamma spectrometry to determine their radium content. A comparison of the different degree of disequilibrium of radon, defined as the ratio between the actual and the secular equilibrium-with-radium soil radon concentration, found at the different sites and depths is presented. The influence on the result of soil type and climate is briefly discussed.