Measurements of thoron and radon progeny concentrations in Beijing, China.

It has been reported that thoron levels in China are above the world average and may therefore make a significant contribution to the natural background radiation dose. We therefore conducted a pilot study of concentrations of both thoron and radon progeny during the spring of 2006 in the Beijing area, China. A new type of portable 24 h integrating monitor with a CR-39 detector was used during the survey. Seventy dwellings and eight outdoor sites were measured during the survey. For country houses built of red bricks and slurry, the average equilibrium equivalent concentrations (EEC) of thoron and radon were 1.02 +/- 0.48 and 16.41 +/- 9.02 Bq m(-3), respectively, whereas for city dwellings built of cement blocks and floor slabs, the results were 0.48 +/- 0.47 and 11.50 +/- 6.99 Bq m(-3) for thoron and radon, respectively. For outdoor air, concentrations of thoron and radon progeny were 0.29 +/- 0.28 and 7.05 +/- 2.68 Bq m(-3), respectively. Radiation exposures from thoron and radon progeny were also evaluated; the ratio of dose contribution from thoron progeny to that of radon progeny was evaluated to be 28% and 17% in country houses and city dwellings, respectively.