Filtration approach to mitigate indoor thoron progeny concentration

Enhanced thoron (220Rn) concentrations reported in Chinese traditional clay dwellings [18, 21], Japanese traditional mud houses [3, 6], Italian tuff and pozzolana buildings [16, 17] and some other potential high risk areas [19] have caused some attention. The decay products of thoron, both attached and unattached fractions, have high potential alpha energy per activity which contributes to a distinct inhalation exposure [23]. Increasing reports point out that the ratio of effective dose from thoron and its progeny to that from radon, thoron and their progeny in some cases accounts for 20% [26], 38% [18] and 55% [7]. Thereby, the exploration on controlling the thoron decay products has practical significance. There are some existing reports about the mitigation of radon and its decay products [2, 8, 10, 14, 25], while scarce literature on the active mitigating of thoron decay products exists. For radon, there are several techniques to minimize the radon concentration, like sub-slab ventilation, foundation drain suction, crawl space ventilation, heat recovery ventilation, sump and sealing, fan-ion generator [1, 4, 9, 12], etc. On the contrary to radon and its progeny, thoron has a very short half-life (56 s), and its most important decay products have longer half-lives (10.6 h, 1 h) compared to the short-lived radon decay products. The consequence is a different activity size distribution in nucleation and accumulation mode of the thoron decay products [5]. The mitigation approach and its effectiveness might therefore differ. Filtration approach to mitigate indoor thoron progeny concentration Jin Wang, Oliver Meisenberg, Yongheng Chen, Erwin Karg, Jochen Tschiersch