Unattached fraction measuring technique and radon lung dose

We examined the influence of measurement techniques used to characterize the ultrafine fraction of airborne radon progeny on the estimation of dose rate received by the lungs by comparing simultaneous measurements of the unattached fraction and the full activity-weighted size distribution. The unattached fraction was measured using a single stainless steel-wire-mesh screen (50% penetration for 4 nm equivalent diameter particles). The full activity-weighted size distribution was measured using a graded-screen array (six stages with equivalent particle diameter for 50% penetration ranging from 0.5 to 500 nm). Thirty paired samples were taken outdoors in a rural location in central New Mexico, USA. Using current exposure-dose conversion factors based on the ICRP 66 Lung Model, we compared the calculated effective dose rate for the respiratory tract for each sample pair. On average, the dose calculated from the full radon-progeny particle-size distribution (graded-screen array measurements) was 80% higher than that calculated from the single-screen measurements. Our results raise questions about the accuracy (i.e., potential low bias) of retrospective dose estimates for miners and other radon-exposed groups for whom the dose assessment was based on the nominal unattached fraction measured with a single screen.