Measurement techniques of radon and its associated radionuclides and their relevant problems

Abstract

  The following problems on radon face us: establishment of the dose assessment, exposure due to thoron and technologically-enhanced exposure due to radon/thoron based on human activities. The radon problem has not yet been solved. When estimating dose, two different approaches are used for assessment. One is an epidemiological approach. In the epidemiological approach, the dose is derived from the relationship between the alpha exposure, i.e., the potential alpha energy concentration and the estimated excess relative risk for lung cancer among miners. The other is a dosimetric approach. The dose is derived from laboratory investigation in this case. There is a three-time difference between the two. It is obvious that information on the particle size of radon progeny is indispensable for accurate dose assessment. In order to combine the two estimates from the two approaches, both mine and home aerosols should be sufficiently characterized. As the second problem, recent studies have shown that attention must be paid to thoron because high thoron concentrations were occasionally observed in some areas. Although most of passive radon detectors are generally designed to minimize the entry of thoron, some of them were affected by the presence of thoron. It is important to understand the performance of the detector with an adequate thoron exposure facility before practical use. As the third problem, radon/thoron concentrations might be enhanced in a closed environment. In this circumstance, their concentrations should be mitigated with proper countermeasures. Building materials can be recognized as the their sources. Exhalation rates of radon and thoron from walls were measured in a traditional Japanese wooden house where a high thoron concentration was observed. No radon exhalation was detected but thoron exhalation rate was as high as that from soil. The dose due to thoron progeny cannot be ignored in such indoor environment.