It is necessary to establish a reference atmosphere in a thoron chamber containing various ratios of Bi-212 to Pb-212 activity concentrations (C(Bi-212)/C(Pb-212)) to simulate typical environmental conditions (e.g., indoor or underground atmospheres). In this study, a novel method was developed for establishing and controlling C(Bi-212)/C(Pb-212) in a thoron chamber system based on an aging chamber and air recirculation loops which alter the ventilation rate. The effects of main factors on the C(Bi-212)/C(Pb-212) were explored, and a steady-state theoretical model was derived to calculate the ratio. The results show that the C(Bi-212)/C(Pb-212) inside the chamber is mainly dependent on ventilation rate. Ratios ranging from 0.33 to 0.83 are available under various ventilation. The stability coefficient of the ratios is better than 7. The experimental results are close to the theoretical calculated results, which indicates that the model can serve as a guideline for the quantitative control of C(Bi-212)/C(Pb-212). (C) 2017 Elsevier Ltd. All rights reserved.
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