Radon and thoron concentration in relation to their decay products in soil

Radon, thoron and their progenies are measured indoors since they represent a health risk for inhalation. Some researchers claim that radon is a natural tracer useful in geosciences, e.g. as an earthquake precursor, which can be passively measured using Lr-115 detectors inside diffusion chambers. However, the Lr-115 covered with an absorbing foil, called direct progeny sensor (DRPS or DTPS), may register radon and thoron progenies. The aim of this work is to evaluate the relationship between concentrations of the radioactive noble gases and their progeny concentrations, in the airborne and deposited states, within PVC pipes buried in the ground. For this purpose, several pinhole twin-chamber single entrance dosimeters have been used for simultaneous measurements of radon and thoron. Following the technique of DRPS and DTPS, we used two detectors Lr-115 covered with 24μm and 36μm aluminium foils, instead of the commonly used aluminized Mylar, in order to register alpha particles of 214Po and 212Po, respectively. These devices were placed on the top of each twin-chamber. One twin-chamber with two Lr-115 detectors inside them and two modified direct progeny sensors on the twin chamber were placed at the bottom of the PVC tube buried in the ground at a depth of 80 cm. Tubes were kept covered with a lid at the top during the measurement period. Among results, the equilibrium equivalent concentration of radon and thoron (EERC and EETC), and the Lr-115 detector response in the DRPS/DTPS devices are given.