Radiation exposure due to 222Rn, 220Rn and their progenies in three metropolises in China and Japan with different air quality levels.

Radiation exposure due to radon contributes most of the ionizing radiation exposure to people among natural radiation sources. This research measured the 222Rn, 220Rn by the RADUET and their progeny concentrations by the improved deposition based 222Rn and 220Rn progeny monitor, and the contribution of outdoor PM2.5 concentrations to indoors by a modified steady-state mass balance model in Beijing, Changchun, China and Aomori, Japan. Based on these results, we preliminarily explored the relevance between the city level outdoor PM2.5 exposure and indoor 222Rn, 220Rn inhalation exposure in these three metropolises with different air quality levels. The average equilibrium equivalent radon concentration (EERC) and equilibirum equivalent thoron concentration (EETC) indoor were 17.2 and 1.1 Bq m-3 in Beijing, 19.4 and 1.3 Bq m-3 in Changchun, and 10.8 and 0.9 Bq m-3 in Aomori, respectively. The indoor EERC and EETC in Beijing showed 1.4 and 2.2 times as high as that measured in 2006. The indoor radiation dose due to inhalation presented in a descending order as Changchun, Beijing and Aomori, which were in accordance with their outdoor 222Rn concentrations. The indoor radiation doses due to 220Rn contributed 30% of the total dose in the three cities, indicating that 220Rn cannot be neglected when evaluating indoor radiation dose. It should be noted that, the indoor PM2.5 concentrations of outdoor origin presented strong correlation (r = 0.772) with indoor EETC and moderate correlation (r = 0.663) with indoor EERC, indicating that the PM2.5 of outdoor origin can break the concentration balance of the indoor PM2.5, then affect the indoor 222Rn and 220Rn behaviors, and further affect the inhalation exposure of radon.

Impact of Wind Speed on Response of Diffusion-Type Radon-Thoron Detectors to Thoron.

Air exchange through a porous medium depends partly on a pressure gradient induced in it, i.e., air-flow conditions of the outer air. Consequently, response of diffusion-type detectors to radon and thoron may vary with air-flow conditions surrounding the detectors. This effect may be significant for thoron measurement because thoron has a shorter half-life than radon. The present study examined response of diffusion-type detectors (RADUETs and one AlphaGUARD) to thoron with respect to wind speed using a thoron calibration chamber. Response of RADUETs to thoron increased with wind speed. Response of the AlphaGUARD increased with wind speed, but it became constant at a high wind speed. Different response trends to thoron between the RADUETs and the AlphaGUARD could be qualitatively explained by flow states induced by the pressure gradient in the filter or the sponge of these detectors. For RADUETs, laminar (Darcy) flow was induced in the sponge in the examined wind speed range, which meant that thoron entry into the detector increased with wind speed. For the AlphaGUARD, laminar flow was induced in the filter in the low wind speed range, whereas flow was changed to turbulent (non-Darcy) flow at a high wind speed for which thoron entry into the detector did not depend on wind speed.