Sensitivity to Thoron on Passive Radon Detectors

INTRODUCTION Although a lot of studies on radon have been done for a long time, there are few reports on thoron. It was considered that the presence of thoron could be negligible because of its own quantity compared to that of radon. However, recent studies have shown high thoron levels in our living environment (1-4). In particular, high thoron concentrations were occasionally observed in some areas, Japan (1,2). This fact made it clear that some of passive radon detectors were sensitive to the presence of thoron. They are commonly used for indoor radon surveys. It is possible that such detectors will give false values unless they are placed properly. Therefore, it is important to understand the detector response to thoron before practical use. A compact thoron chamber system was set up for the purpose. In this study, the followings are shown: configuration of the thoron chamber and sensitivity to thoron of several passive radon detectors.