Intercomparison of retrospective radon detectors

We performed both a laboratory and a field intercomparison of two novel gla ss-based retrospective radon detectors previously used in major radon case- control studies performed in Missouri and Iowa. The new detectors estimate retrospective residential radon exposure from the accumulation of a long-li ved radon decay product, Pb-210, in glass. The detectors use track registra tion material in direct contact with glass surfaces to measure the alpha-em ission of a Pb-210-decay product, Po-210. The detector's track density gene ration rate (tracks per square centimeter per hour) is proportional to the surface a-activity. In the absence of other strong sources of alpha-emissio n in the glass, the implanted surface alpha-activity should be proportional to the accumulated Po-210, and hence to the cumulative radon gas exposure. The goals of the intercomparison were to a) perform collocated measurement s using two different glass-based retrospective radon detectors in a contro lled laboratory environment to compare their relative response to implanted polonium in the absence of environmental variation, b) perform collocated measurements using two different retrospective radon progeny detectors in a variety of residential settings to compare their detection of glass-implan ted polonium activities, and c) examine the correlation between track densi ty rates and contemporary radon gas concentrations. The laboratory results suggested that the materials and methods used by the studies produced simil ar track densities in detectors exposed to the same implanted Po-210 activi ty. The field phase of the intercomparison found excellent agreement betwee n the track density rates for the two types of retrospective detectors. The correlation between the track density rates and direct contemporary radon concentration measurements was relatively high, considering that no adjustm ents were performed to account for either the residential depositional envi ronment or glass surface type. Preliminary comparisons of the models used t o translate track rate densities to average long-term radon concentrations differ between the two studies. Further calibration of the retrospective de tectors' models for interpretation of track rate density may allow the pool ing of studies that use glass-based retrospective radon detectors to determ ine historic residential radon exposures.