Long-Term Measurements of Equilibrium Factor and Unattached Fraction of Short-Lived Radon Decay Products in a Dwelling - Comparison with Praddo Model

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 1993), the dose due to the inhalation of radon decay products represents almost 50% of the total natural radiation dose to the general population. The scientific community is interested in the assessment of the risk induced by domestic radon exposure. The dosimetric models used to estimate the dose are very sensitive to unattached fraction and size distributions, which makes the characterization of the indoor radon decay products aerosol necessary. For this purpose, longterm measurements of unattached fraction (f_p ) and equilibrium factor (F) were taken in a dwelling under typical indoor domestic aerosol conditions. An original device consisting of an annular diffusion channel set in parallel with an open filter was developed and calibrated to continuously measure the unattached fraction. Moreover, radon activity concentration and particle concentration were simultaneously monitored. With aged aerosol, particle concentration was found to be very low (between 500 and 5000 cm^-3), radon activity concentration ranged from 240 to 2800 Bq m^-3, and the mean values of f_p and F were, respectively, 0.31 (0.08-0.67) and 0.16 (0.04-0.45). With aerosol sources, the high increase in particle concentration led to a negligible unattached fraction and raised the equilibrium factor. A correlation relationship was determined between these two parameters under different aerosol conditions. Finally,our experimental results were compared to results obtained with the PRADDO model; this comparison showed a good agreement between these two different approaches.