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 means of the measurement ofthe Po-210 surface activity is subject to various uncertainties. These result partly from the valuesassumed for the equilibrium factor F and for the unattached fraction f, and, more importantly, fromdifferences in the deposition velocities of short-lived decay products of Rn-222, caused by varyingconditions of turbulence. In order to evaluate the actual range of the variation which occurs underGerman living conditions, measurements for the deposition velocity parameter were carried out inseveral dwellings in which increased levels of radon were present. The statistical evaluation of themeasurements produced a mean deposition velocity of 1.7 m/h for Po-218 and 0.4 m/h for Pb-214, anda relative standard deviation in the measured values of as low as approximately 50%. This laysignificantly below the uncertainty value expected from the literature and would seem to justify theretrospective determination of the radon exposure from Po-210 surface activity measurement for usein, for example, epidemiological studies