Uncertainty evaluation in radon concentration measurement using charcoal canister

•Measurement uncertainty budget for radon activity concentration established.•Three different methods for ROI selection are used and compared.•Recommend to use one continuous ROI, less sensitive to gamma spectrometry system instabilities.

Active charcoal detectors are used for testing the concentration of radon in dwellings. The method of measurement is based on radon adsorption on coal and measurement of gamma radiation of radon daughters. The contributions to the final measurement uncertainty are identified, based on the equation for radon activity concentration calculation. Different methods for setting the region of interest for gamma spectrometry of canisters were discussed and evaluated. The obtained radon activity concentration and uncertainties do not depend on peak area determination method.