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Activated charcoal was widely used in radon researches and mitigation applications because of good adsorption ability. In the paper, a simple model that can predict radon removal efficiency (η) for radon mitigation applications using flow-through activated charcoal system was developed based on the previous works. Experiments were conducted with a flow-through activated charcoal system to validate the model and study the influence of factors on η. The experimental results of η are consistent with the theory to within 4% at the flow rates of 1–3 L/min, but range from 2% to 14% at the flow rates of 4–5 L/min. The equilibrium time of radon linearly decreases with rising flow rate, and η decreases with rising flow rate. With moisture competing with radon for adsorption sites on the activated charcoal, radon reaches the equilibrium concentration more quickly than moisture does. As relative humidity increases, η decreases, but the radon equilibrium concentration increases. The values of η are bigger for those smaller particle sizes with the same type of activated charcoal. The results of this paper are useful for designing activated charcoal systems at indoor environmental conditions and predicting η for radon mitigation applications.

The monitors used to measure radon concentration must be calibrated, and the calibration factor of each measurement cycle should be determined. Thus, the determination time of calibration factors of NRL-II radon monitors should be reduced. In this study, a method is proposed to determine the calibration factors of radon monitors rapidly. In the proposed method, the calibration factor is initially determined in the 60-min measurement cycle; the calibration factor is then identified in the other measurement cycle on the basis of the principle that the calibration factor of the same radon monitor in different measurement cycles is inversely proportional to the number of α particles produced by 218Po decay in this cycle. Results demonstrate that the calculated calibration factor of the different measurement cycles is consistent with the experimental calibration factor. Therefore, this method is reliable and can be used to determine the calibration factor of radon monitors rapidly.

The simultaneous radon and thoron monitoring method developed at University of South China was adopted to survey radon and thoron concentrations in two types of countryside dwellings with the soil walls or the red brick walls in two villages of Hengyang City. The measurement results indicate that more attention must be paid to the risk of environmental thoron in countryside dwellings, because the effective dose from thoron and its daughters is almost equal to or bigger than that from radon and radon daughters in some dwellings with the soil walls.

We analyzed the vertical long distance migration experiment data of radon and its daughters,and found that the number of α particles is insufficient to explain the fast upward migration of radon by helium- radon clustering. If assume that radon has very strong ability to adsorb the helium from the air to form helium-radon clusters for vertical migration, then there is an inconsistency between the tentative and that experimental conclusion,that the upward and downward migration probability of radon and its daughters in natural state is equal to that when helium gas is added.So we propose that helium- radon clustering may not be the main reason of radon and its daughters′ fast upward migration. There may be other more complex reasons. The phenomenon needs further research.