Two new 222Rn emanation sources – a comparison study

Abstract. More than 50 % of naturally occurring radiation exposure to the general public is due to the noble gas radon (222Rn) and its progenies, causing considerable health risks. Therefore, the European Union has implemented Council Directive 2013/59/EURATOM to measure 222Rn activity concentrations and to identify radon priority areas (RPAs) to specify areas where countermeasures are most needed. Although 222Rn measurements are far spread across Europe, traceability to the International System of Units (SI) is still lacking for radon activity concentrations below 300 Bq m−3. Consequently, measurement results cannot be reliably compared with each other. The European Metrology Research Programme for Innovation and Research (EMPIR) 19ENV01 traceRadon project aimed to address this issue and has developed two new 222Rn emanation sources, intended to be used as calibration standards for reference instruments. The goal of this paper is to investigate and compare the two sources to ensure their quality by comparing the calibration factors estimated from both sources for the same reference instrument. This was done for three reference instruments in total at two experimental sites. Differences in calibration factors for one reference instrument of up to 0.07 were derived. Despite the small differences between the calibration factors, all uncertainties are well within the intended target uncertainty of 10 % for k = 1.