Abstract: Radon is the major components of the natural radiation background, and radon measurement is important for radiation environmental monitoring. Radon chamber, used for the calibration and performance check of radon monitors, plays an important role during the procedure of quality control for radon measurement. Conventional radon chamber generally consists of standard radium sources and volume for controlling radon concentration and humidity. While permission and safety management of standard radium source make conventional radon chambers difficult to develop and widely use. On the basis of the characteristics of soil gas which has high and stable radon concentration, a humidity controllable radon chamber system based on soil-radon is designed and constructed. This radon chamber system realizes the control of radon concentration by mixing air with soil gas in different fraction, and that of humidity by refrigeration type dryer. The research of radon chamber system made by Peking University shows the radon concentration and relative humidity can be controlled from 826-5 852 Bq/m³, and 30.8%-70.6%, respectively, and both of them can be stable for over 40 hours. This radon system gets rid of the limitation of radium sources, and is easy to be constructed and realized. It provides a possible way for in-situ calibration for radon monitors and can be widely used on quality control for radon measurement.

Key words: radon chamber, radon gas, radon in soil, humidity control, radon concentration control