Plate-out and implantation of 222Rn decay products in dwellings

Abstract

Airborne radon ( 222Rn) decay products deposit onto all open surfaces in a dwelling. A fraction of the deposited short-lived progenies will be immobilized due to alpha recoil decay implantation. The implanted activity of long-lived radon progenies has two different areas of application, either as a retrospective radon exposure monitor or as a long-term tracer for submicron particle deposition processes. To reveal the surface homogeneity of implanted activity, glass sheets from a dwelling were scanned by collimated pulse ionizing chambers. The scanning of individual glass sheets revealed that the implanted activity is homogeneous within approximately ± 20% over the surface. The surface activity frequently decreases close to the bordering frame, indicating a disruption of the airflow boundary layer. In a pilot study involving 23 detached houses of similar type, the implanted activity of the glass objects correlated well with the estimated radon exposure (r 2=0.55). In one home, the ingrowth of implanted 210Pb in four initially unexposed picture frames was followed for 3 y. In the two deliberately chosen recessed places, the plate-out rate was approximately 40% lower compared to the two openly exposed objects. Larger variations in plate-out rates should be expected near radiators and other airflow generators.