A passive technique to measure radon progeny surface deposition variations in rooms and chambers

摘要

When the alpha track detectors CR-39 and LR-115 are simultaneously exposed to air containing radon and its progeny, the CR-39 will record alpha activity from both radon progeny deposited on its surface and also from radon gas and its progeny in the air above its surface. The LR-115 will only record tracks from alpha particles emitted from radon and its progeny in a restricted volume of air above its surface because of its narrower alpha energy range response compared to that of CR-39. For the same reason, LR-115 will not record tracks from the 6.00 MeV and 7.68 MeV alpha particles emitted by progeny deposited on its surface as these energies are above its registration threshold. This latter characteristic of LR-115 is exploited in the work described here. A series of laboratory exposures were carried out in which it was possible to separately determine the relative responses of both CR-39 and LR-115 to the three alpha emitters ~(222)Rn, ~(218)Po and ~(214)Po in the air. It is then possible to obtain a value for the alpha track density contribution due only to progeny deposited on its surface by using the LR-115 track density and the three relative response ratios to subtract the contributions of the airborne activities from the total track density on the CR-39 detector. This technique was applied in some Dublin dwellings and the results are reported here. With the increased current interest in the use of surface trap measurements of ~(210)Po on glass as a means of retrospectively assessing radon exposure in epidemiological studies, the availability of the technique presented here may prove to be both timely and useful in improving the accuracy of such retrospective radon exposure assessments.