Temperature and humidity consideration for calculating airborne 222Rn using activated charcoal canisters

A radon calibration chamber with variable and controlled radon concentration, humidity, and temperature was constructed and used to extend the calibration range of open-faced and diffusion-barrier charcoal canisters for higher temperature and humidity applications. The optimum exposure time to achieve the best detection accuracy and the lowest minimum detectable level was between 2 and 4 d depending on relative humidity for open-faced canister and 4 d for diffusion barrier canister over a range of humidity. The dependence of radon adsorption on the temperature was also studied for both types of canister at different values of relative humidity. The open-faced canisters at 15 degrees C absorb 68% more radon than at 30 degrees C over the range of humidity from 20% to 80%. The diffusion-barrier canister shows insignificant variation in absorption over the same range of temperature and humidity.