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 Atom ic Radiation (UNSCEAR 1993), the dose due to the inhalation of radon decay products represents almost 50% of the total natural radiation dose to the g eneral 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 di stributions, which makes the characterization of the indoor radon decay pro ducts aerosol necessary. For this purpose, longterm measurements of unattac hed fraction (f(p)) and equilibrium factor (F) were taken in a dwelling und er typical indoor domestic aerosol conditions. An original device consistin g of an annular diffusion channel set in parallel with an open filter was d eveloped and calibrated to continuously measure the unattached fraction. Mo reover, radon activity concentration and particle concentration were simult aneously monitored. With aged aerosol, particle concentration was found to be very low (between 500 and 5000 cm(-3)), radon activity concentration ran ged from 240 to 2800 Bq m(-3), and the mean values of f(p) and F were, resp ectively, 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 frac tion and raised the equilibrium factor. A correlation relationship was dete rmined between these two parameters under different aerosol conditions. Fin ally, our experimental results were compared to results obtained with the P RADDO model; this comparison showed a good agreement between these two diff erent approaches.