Prototype of a primary calibration system for measurement of radon activity concentration

To calibrate measurement devices for monitoring the activity concentration of Rn-222 in air, a prototype of a calibration facility is tested using a solid Ra-226 source and a high-purity germanium (HPGe) detector. An emanation box was mounted on the detector for online gamma measurements. Inside this box, a 32.8 kBq +/- 3% Ra-226 standard source was placed. An AlphaGUARD control radon monitor was connected to the emanation box with a pumping air system in an open flow mode as a reference monitor. The emanation coefficient of the source was controlled online by comparing the gamma activity of Bi-214 (Ey=609.3 key), progeny of Ra-226, to that of the calibration source. A standard Cs-137 source, installed within the emanation box, was used as a reference for gamma spectroscopy using the HPGe detector, with a total systematic error of 4% and a random error less than 2%. The ratio between gamma measurements and AlphaGUARD was 0.94 +/- 0.4; which is within the 9% uncertainties of AlphaGUARD calibration. (C) 2015 Elsevier Ltd. All rights reserved.