Quantification of the response delay of mobile radon-in-air detectors applied for detecting short-term fluctuations of radon-in-water concentrations

Abstract

Radon-in-water concentration time-series that are detected by means of radon-in-air detectors usually demonstrate a distinct response delay between radon-in-water concentration and the related radon-in-air records. This response delay results in recorded radon-in-air time-series that are not fully reflecting short-term radon-in-water fluctuations. The response delay is due to (i) the water/air transfer kinetics of radon and (ii) the delayed decay equilibrium between ²²²Rn and its progeny ²¹⁸Po, which is actually being measured by most radon-in-air monitors. In the discussed study we designed a laboratory experiment with a defined radon-in-water input function, recorded the radon-in-air response signal and analysed the two time-series. Radon-in-air records showed a delay of ∼10 min relative to the radon-in-water concentrations. However, for reconstructing the original radon-in-water signal based on the detected radon-in-air time-series we developed a numerical model considering all delay causing parameters. It was shown that the applied model allows reconstructing the input signal without any time delay and with correct concentrations for all concentration fluctuations lasting longer than about 10 min. In conclusion we can state that the developed numerical model allows a precise determination of radon-in-water concentration time-series based on radon-in-air records even if short-term fluctuations (>10 min) occur.