222Rn and 220Rn concentrations in selected soils developed on the igneous rocks of the Kaczawa Mountains (Sudetes, Poland)

This study presents the preliminary results of 222Rn (radon) and 220Rn (thoron) concentrations that were measured in the soils developed on igneous rocks including mafic (pillow lavas, basalts and melaphyre) and acid (keratophyre, rhyolite and rhyolitic tuff) rocks at ten locations in the Kaczawa Mountains (SW Poland). The measurements were carried out at sampling depths of 10, 40 and 80 cm using a RAD7 portable radon system. The highest concentrations of radon (222Rn) were mainly observed in the soils overlaying acid igneous rocks. The highest value of 11 kBq m-3 was obtained at a depth of 10 cm for soils overlaying melaphyre. At depths of 40 and 80 cm, the averages of 222Rn concentrations showed the same values of 3.6 kBq m-3 for all of the soils investigated. The highest concentrations of thoron (220Rn) were observed in soils overlaying acid igneous rocks, i.e. the value of 49 kBq m-3 at a depth of 40 cm for soils overlaying rhyolitic tuff. In the soils developed on basalts, the average concentrations of 222Rn increased with the sampling depth, whereas the average concentrations of thoron (220Rn) decreased with increasing sampling depth. Positive correlations were found between 232Th activity in the parent rocks and soil gas 220Rn concentrations at all of the sampling depths, whereas a positive correlation between soil gas 222Rn and the 238U activity concentration in the parent rocks was only found at a depth of 40 cm