Response of a Radon Charcoal Cannister to Climatic and Radon Variations in the Inte Radon Chamber

Charcoal canisters are commonly used to measure radon concentration for periods of 2-7 days. The radon absorption and desorption process is known to be sensitive to several environmental parameters such as temperature, relative humidity and radon concentration fluctuation. In the present study a set of exposures under different environmental conditions were done in the INTE radon reference chamber in order to evaluate the response of a canister, designed by the INTE, to relative humidity, temperature and radon concentration. A 3-day period was chosen for the 11 exposures carried out at relative humidities, temperatures and radon concentrations ranging from 30-80 %, 10-30 oC and 400-10000 Bq m, respectively. In each run 6 canisters were exposed in order to achieve a good level of statistical resolution. The climatic response analysis shows that for a constant temperature of 20 oC, radon is absorbed about 25 % more efficiently at a relative humidity of 30 % than at a relative humidity of 80 %. For a constant humidity of 50 %, radon is absorbed about 50 % more efficiently at 10 oC than at 30 oC. Since the increase in the canister mass during exposure is due to water absorption, a correction in the calibration factor has been estimated for different relative humidities by measuring the weight increment, before and after exposure. The response of the detector at different, but constant, radon concentration levels shows no influence on the calibration factor value. However, when radon concentration fluctuated during the 3day period, the weight of the first day compared with the total exposure period is about 15%, that of the second day is 30 % and that of the last day 55%.