Integrating Measurements of Indoor Thoron and Its Progeny Concentrations

INTRODUCTION UNSCEAR (1) reported that the effective doses due to inhalation of radon (Rn) and its progeny account on average for about one-half of all natural sources of radiation. In recent years, indoor surveys in Europe and Asia revealed that the dose contribution from thoron (Rn) and its progeny can equal to or even exceed that of Rn and its progeny (2). For assessment the public exposure from Rn and its progeny, large-scale surveys of indoor Rn and its progeny concentrations are desirable. Recent reviews of Rn and its progeny metrology can be found in literature (2, 3). However, convenient, low-cost and time-integrating measuring methods which are suitable for large-scale surveys are still few. In indoor environments, the air mixing time is usually much larger than the half-life of Rn (56 s), the Rn concentration is highly non-uniform, so it is difficult to obtain a representative value of indoor Rn concentrations. Moreover, from the view of dose contribution, Rn progeny are much more important than Rn. Therefore, it is desirable to know the concentrations of Rn progeny. In this study, three integrating measurement methods with allyl diglycol carbonate plastic (CR-39) as detectors were attempted, and a smallscale of field measurement was performed. The results indicate that they may be suitable for evaluating the indoor Rn and its progeny concentrations whenever the public exposure to Rn and its progeny is taken into account.