Measurements of deposition velocity of radon decay products for examination of the correlation between air activity concentration of radon and the accumulated Po-210 surface activity

The retrospective determination of radon exposure levels in dwellings by me ans of the measurement of the Po-210 surface activity is subject to various uncertainties. These result partly from the values assumed for the equilib rium factor F and for the unattached fraction f(p), and, more importantly, from differences in the deposition velocities of short-lived decay products of Rn-222, caused by varying conditions of turbulence. In order to evaluat e the actual range of the variation which occurs under German living condit ions, measurements for the deposition velocity parameter were carried out i n several dwellings in which increased levels of radon were present. The st atistical evaluation of the measurements produced a mean deposition velocit y of 1.7 m/h for Po-218 and 0.4 m/h for Pb-214, and a relative standard dev iation in the measured values of as low as approximately 50%. This lay sign ificantly below the uncertainty value expected from the literature and woul d seem to justify the retrospective determination of the radon exposure fro m Po-210 surface activity measurement for use in, for example, epidemiologi cal studies. (C) 2001 Elsevier Science B.V. All rights reserved.