Adsorption of 222Rn by open-faced and diffusion-barrier canisters at different conditions of temperature and humidity.

Open-faced and diffusion-barrier charcoal canisters were individually exposed to a fixed temperature, humidity, and radon concentration in a chamber for a period of 7 d. The radon progeny activity in the canister under study was measured every 3 h. A total of 15 runs were made for the open-faced canisters and nine runs for the barrier canisters with temperatures and absolute humidities ranging from 15-30 degrees C and 0-15 g m-3, respectively. In addition, several runs were made with the radon, temperature, and humidity changing during the 7 d. Results show that open-faced canisters adsorb radon up to 60% more efficiently at 15 degrees C than at 30 degrees C while the barrier canisters show little temperature dependence. The barrier canisters are much less sensitive to humidity effects than the open-faced canister. When used to measure the radon concentration in air, the open-faced canister integrates over a period of only approximately 48 h while the barrier canister integrates over a period of approximately 96 h. The short integration time and the interference of water adsorption by open-faced canisters indicate that the open-faced canisters should be used for exposure times of 48 h and no longer.