Mixed exposures to radon and thoron for cave residents at Chinese loess plateau

In order to understand biological effects of human beings caused by indoor radon exposure, radiation measurements were comprehensively made in cave dwellings were widely distributed at Chinese loess plateau. In those measurements, radon, thoron and equilibrium equivalent thoron concentration were determined in each house throughout one year. Radon and thoron concentrations were measured with a newly designed passive radon-thoron discriminative monitor. The equilibrium equivalent thoron concentration was measured with the deposition rate measurement technique. These devices were placed in each house for 6 months and were replaced with new ones for another 6 months. To obtain reliability of environmental data for the long-term measurement, active measurements were accordingly carried out during this observation period. For radon progeny measurement, an alpha spectroscopic method was used with grab sampling. For thoron progeny measurement, on the other hand, a simple but newly developed measurement technique was adopted with the alpha-track registration on the CR-39 detector. Using the data obtained over one year, those results were categorized with housing structure and were statistically analyzed. Compared to other studies conducted at Chinese loess plateau, the present study has shown that the radon concentration is not so high as them, the presence of thoron is significantly detected but the magnitude of thoron progeny concentration is small