Radon and thoron in cave dwellings (Yan'an, China)

Wiegand, J; Feige, S; Xie, Quingling; Schreiber, U; Wieditz, K; Wittmann, C; Luo, Xiarong

University of Essen, Department 9-Geology, Universitaetsstrasse, 45141 Essen, Germany, [mailto:jens.wiegand@uni-essen.de]

Health Physics [Health Phys.]. Vol. 78, no. 4, pp. 438-444. Apr 2000. ISSN 0017-9078

super(222)Rn and super(220)Rn concentrations were measured in cave dwellings and brick houses in the region of Yah'an (China) during summer 1997. The underground dwellings are built into Quaternary loess, and all investigated houses are founded on it. The median values of indoor super(222)Rn and super(220)Rn concentrations are 42 (n = 18) and 77 Bq m super(-3) (n = 15) for brick houses and 92 (n = 23) and 215 (n = 17) Bq m super(-3) for cave dwellings. To classify the dwellings in respect to their "cave-character," the fraction of walls having a direct contact to the loess is calculated for each dwelling. While the super(222)Rn concentrations are increasing with higher fractions, the super(220)Rn concentrations are not correlated with this fraction. On the other hand, due to the short half-life of super(220)Rn the distance from the measuring point to the walls is negatively correlated with the super(220)Rn concentration, while there is no correlation with the super(222)Rn concentration. Therefore, concentric isolines of super(220)Rn concentrations showing a strong gradient were detected in cave dwellings. An influence of the ventilation rate is distinct for super(222)Rn but weak for super(220)Rn. The effective dose rates for super(222)Rn and super(220)Rn and their progenies are calculated for brick houses (2.7 mSv y super(-1)), cave dwellings (7.1 mSv y super(-1)), and for traditional cave dwellings with a bed foundation built with loess (16.7 mSv y super(-1)). These calculations are based on summer measurements only. It is expected that the true effective dose rates will be significantly higher.