Estimating long-term radon concentrations from surface-embedded 210PO

A fraction of the indoor radon progeny that reach room surfaces are embedded by radioactive recoil. One radon daughter, 210Pb, is long-lived and, over the years, accumulates on surfaces at a rate proportional to the radon concentration. The amount of 210Pb can be measured through the alpha activity of its progency, 210Pb. Thus, the average radon concentration curve of integrated exposure versus activity, and the glass exposure time. We have found in the laboratory and homes, that surface alpha activity has a strong linear relationship to integrated exposure, over a wide range of data. Two systems suitable for measurements in homes have been developed. For rapid results, a large area PIPS detector is coupled to a portable MCA. This can collect enough counts in a day to estimate radon exposure at accuracies of ±50% in a 10 year-old home with an average radon concentration of 4 pCi/L. This compares quite favorably with the accuracy (±80 to 150%) estimates based on standard short-term measurement techniques. We have also developed a track-registration detector, suitable for mass distribution, that simultaneously measures glass surface activity, contemporary radon concentration, and surface progeny deposition rates