Weihai Zhuo

Up-to-date radon-thoron discriminative detector for a large scale survey

An up-to-date radon-thoron discriminative detector has been developed for conducting a large scale survey. Comparing with our previous detector, some functional problems have been solved. The lowest and highest detection limits of the detector were estimated to be around 5 and 1000Bqm−3 for radon, and 15 and 1000Bqm−3 for thoron, respectively, with a 6month exposure and several theoretical assumptions. Small indoor survey were carried out in Japan and in Hungary using the present detector. The presence of thoron was demonstrated in any indoor surveys by the two results. Since any measurements without discrimination of radon isotopes will result in different risk estimates from actual situations, a special attention should be paid to thoron and its concentration should be accordingly measured as well as the radon concentration.

A simple passive monitor for integrating measurements of indoor thoron concentrations

A simple passive monitor was developed for integrating measurements of indoor thoron concentrations. The monitor was remodeled from a commercially available radon monitor with allyl diglycol carbonate (CR-39) detector. By adding four holes (φ=12 mm) and covering them with high permeability of filter paper, the air exchange rate of the monitor was largely enhanced. The technical characteristics of both the radon and thoron monitors were examined through calibration experiments. A high conversion factor of 1.32±0.14 tracks cm−2⋅(kBq m−3 h−1)−1 and the low lower detection limit for thoron measurements provide the essential conditions for measuring thoron more precisely and sensitively. Furthermore, the main physical advantages of the monitor are its simple construction, light weight, and compactness as well as its low cost, which are preferable for large-scale and long-term indoor surveys. Simultaneous measurements of both indoor thoron and radon are indispensable for accurate assessments of public exposure ...

Radon–Thoron Discriminative Measurements in Gansu Province, China, and Their Implication for Dose Estimates

Indoor radon measurements were carried out in cave dwellings of the Chinese loess plateau in Gansu province, where previously the Laboratory of Industrial Hygiene (LIH), China, and the U.S. National Cancer Institute (NCI) had conducted an international collaborative epidemiological study. The LIH–NCI study showed an increased lung cancer risk due to high residential radon levels, and estimated the excess odds ratio at 100 Bq/m3 to be 0.19 (Wang et al., 2002). The present study used two types of newly developed passive monitors: One is a discriminative monitor for radon and thoron; the other is a selective monitor for thoron decay products. The arithmetic mean concentrations of indoor radon and thoron were 91 and 351 Bq/m3, respectively. As reported by our previous study in Shanxi and Shaanxi provinces (Tokonami et al., 2004), the presence of high thoron concentration was confirmed and thoron was predominant over radon in the cave dwellings. However, the mean equilibrium equivalent thoron concentration (EETC) was found to be much lower than expected when assuming the equilibrium factor of 0.1 provided by the UNSCEAR (2000) report. The effective dose by radon and thoron decay products was estimated to be 3.08 mSv/yr. It was significantly lower than the dose of 8.22 mSv/yr estimated from the measurements that did not take into consideration any discrimination between radon and thoron. Excess relative risk of lung cancer per sievert may be much higher than the risk estimated from the LIH–NCI study, considering that discriminative measurements were not used in their study.

Natural radiation levels in Tamil Nadu and Kerala, India

Publisher Summary There are a lot of problems to be solved to understand the biological effects due to very low-dose radiations. If an epidemiological study is effectively conducted with a small population in the future, high background radiation areas will be suitable for the purpose. The present radiation survey was preliminarily conducted so as to understand the relevant dosimetric quantities taking this future project into account. There was little correlation among the data and they seemed to be independent. The most significant dose arises from gamma radiation because the other dosimetric quantities are much less than the gamma dose. Since there are no epidemiological data on thoron exposure, many problems remain unsolved. The dose assessment for thoron and its decay products has not yet been established as well as that for radon. It can be pointed out that the dose contribution from thoron gas itself should be considered because residents lie almost directly on/near the ground/floor (main source of thoron) when they sleep.

Natural radiation exposures for cave residents in China

Publisher Summary To understand the biological effects on human beings due to natural radiation exposures as a final goal, the following radiation measurements were preliminarily carried out in cave dwellings and their surrounding areas in China (Shanxi and Shaanxi provinces). There are many cave dwellings where the radon concentration seems to be high on the Chinese loess plateau. Since the residential mobility is low, this area will be suitable for conducting a case–control study on lung cancer risk and residential radon exposure. According to the careful strategy, natural radiation measurements were preliminarily made in Shanxi and Shaanxi provinces. The case–control study in Gansu province conducted by NCI has shown that the lung cancer risk increased with increasing radon level. According to survey results from the present study, however, the presence of thoron cannot be negligible. In fact, the radon concentration was much lower than that given by NCI. It seems that there are several problems to be solved and new findings to be of interest.

Integrating measurements of radon and thoron and their deposition fractions in the respiratory tract

Publisher Summary For simultaneous measurements of indoor 222 Rn and 220 Rn and estimation of their deposition fractions in the respiratory tract, a new type of passive integrating 222 Rn and 220 Rn monitor and a portable bronchial dosimeter were developed. The passive 222 Rn and 220 Rn monitor was rebuilt from a commercially available passive 222 Rn monitor. Besides its simple construction, the volume and weight of the new monitor are only 110 cm 3 and 20 g. Calibration factors of 222 Rn and 220 Rn for the new monitor were systematically studied through calibration experiments. Its measuring results are in general agreement with other reported values in ordinary room conditions. The main merits of the new bronchial dosimeter and the associated passive integrating monitors are their compactness, portability and low-cost. These devices are expected to be useful for large-scale dose surveys.