Continuous measurements of soil radon under regular field conditions

Continuous soil radon measurements were pel for med in the frame of an EU-r adon network using the Clipperton II detector. It has been found that in so me periods, soil radon levels obtained with one Clipper ton II probe are ve ry different from those obtained with another probe placed at the same dept h but a short distance apart. Sudden fluctuations of soil radon levels in a given site have been observed as well. To determine whether this behaviour corresponds to the nature of radon gas in the soil or to the detection tec hnique, various experiments have been performed. It has been observed that when different detectors are exposed at the same regular field conditions, their discrepancy is lower than 11%. When the soil radon concentration is a pproximately constant, the statistical fluctuations of the Clipperton probe s are lower than 15%. The application of the Fourier filtering. algorithm t o the rough data, removing all frequency components smaller than 1/24 h(-1) , has led to a complete correlation between different Clipperton II probes. The time response of the probes has been investigated in a specific experi ment at the laboratory. It has been found that the response of the probes t o a sudden change of radon concentration is controlled by the diffusion pro cess along the bottom tube of the probe. Therefore, this study shows that t he experimental data can be attributed to the natural behaviour of soil rad on.