An improved 222Rn canister using a two-stage charcoal system.
A prototype for an improved passive 222Rn canister (R-Canister) was designed and compared to conventional charcoal canisters for its adsorptive and desorptive characteristics following exposures to 222Rn at 23 degrees C in the presence of water vapor. The R-Canister, containing a two-stage charcoal system, minimizes the adverse effects of water vapor by maintaining the amount of adsorbed water vapor in the primary Rn adsorbent below the "break-point" of the charcoal. This is achieved by the placement of a desiccant charcoal cartridge 6 cm above the primary Rn adsorbent. The optimal bed depth of the primary adsorbent, determined from a diffusion study, was found to be 2.3 cm. The measured value for the effective diffusion coefficient of RN in a peat-based charcoal at 15% humidity and 25 degrees C is 7.97 x 10(-10) m2 s-1. Exposures to 70% humidity for 7 d increased the buildup time-constant of Rn in the R-Canisters by 33% as compared to R-Canisters exposed to 15% humidity. At relative humidities ranging from 15-70%, the 222Rn buildup time-constant of the R-Canister ranged from 43-94 h, whereas the desorption time-constant ranged from 46-64 h. Typical buildup time-constants and desorption time-constants for conventional fully-opened charcoal canisters currently in field use ranged from 30-43 h and 17-29 h, respectively, over the same range of humidities.
Scarpitta
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U.S. Department of Energy, Environmental Measurements Laboratory, New York, NY 10014.
Harley
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D000396:Air Pollutants, Radioactive / Q000032:analysis*; D002606:Charcoal; D004867:Equipment Design; D006798:Housing; D011834:Radiation Monitoring / Q000295:instrumentation*; D011886:Radon / Q000032:analysis*
D000396:Air Pollutants, Radioactive; D002606:Charcoal; D011886:Radon