An improved passive activated C collector for measuring environmental 222Rn in indoor air.
A modified version of an activated C monitor has been developed for the time-weighted average measurement of 222Rn for periods ranging from 1-7 d. The new collector consists of a metal can containing 50 g of activated C with a sintered metal filter covering the 3.2-cm diameter sample port in its lid. The new configuration reduces the adsorption and desorption rate of both 222Rn and water vapor by a factor of 4-5, as compared to an open-faced canister. The device measures the average 222Rn concentration accurately, even if the 222Rn concentration varies by more than a factor of 10. For practical situations encountered indoors, the modified collector yields results that are accurate to within +/- 10%. The integration time constant of the collector, tested at relative humidities ranging from 23-75%, is 9-11 d, which is more than three times longer than that of existing diffusion barrier collectors. It is simple to use, inexpensive (total cost of materials is +3.50), maintenance-free, easily sent and returned in the mail (total weight = 100 g), and is reusable for multiple exposures after simple regeneration by heating. The lower limit of detection for a 10-min counting interval is 7 Bq m-3 (0.2 pCi L-1) when counted within 3 d after the end of exposure.
George
A C
AC
Environmental Measurements Laboratory, U.S. Department of Energy, New York, NY 10014-3621.
Weber
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D000327:Adsorption; D000393:Air Pollutants / Q000032:analysis*; D000396:Air Pollutants, Radioactive / Q000032:analysis*; D002244:Carbon; D006283:Health Physics; D006798:Housing; D006813:Humidity; D008433:Mathematics; D011834:Radiation Monitoring / Q000295:instrumentation; D011886:Radon / Q000032:analysis*; D013997:Time Factors
D000393:Air Pollutants; D000396:Air Pollutants, Radioactive; D002244:Carbon; D011886:Radon