Generation and control of radon from soil

In this study, we developed a simple radon generator which can control the radon generated from soil by changing humidity. The weathering granite soil of central Ibaraki prefecture was used as a radon source in this experiment, and the soil particle size was adjusted under 106 μm, using the standard sieve. The humidity of the air was controlled by changing the volume ratio between the dry and humidified air. The air was then introduced into a column packed with the soil sample. Radon emanated from the soil sample was measured using a device of electrostatic collection type (RAD7, Durridge Co. Inc., USA). Radon concentration increased with absolute humidity. This might be because the water adsorbed to the soil particles works as a promoter of radon exhalation up to a certain moisture level. Thoron concentration also has the same tendency as radon and its dependency on absolute humidity was larger than radon. The generation of radon from the soil column was controllable by absolute humidity of supplied air. (author)