Radon chamber functionality: the impact of ventilation rate measurement on the reliability of radon metrology

Radon is the only naturally occurring radioactive gas. Due to its health risk, there is an increasing interest in measuring radon levels in residential, workplace, outdoor, and laboratory environments. In radon laboratories, radon chambers as a controlled environment are used for calibrating radon sources, measuring instruments, and evaluating radon-related parameters in environmental samples. Accurate radon measurement within radon chambers is frequently compromised by uncontrolled removal processes like ventilation rate (or leakage rate) and back diffusion, which affect the reliability of radon metrology. This study aims to evaluate the performance of a medium-sized radon chamber, with a particular focus on the critical importance of measuring its ventilation rate to enhance the accuracy of measurements and calibration conducted within it. A hybrid methodology was used, combining Computational Fluid Dynamics (CFD) for modelling ventilation rates with experimental methods, such as the tracer CO₂ decay method, active (AB-5), and passive (CR-39) radon techniques. For confined geometries with restricted ventilation pathways, CFD analysis reveals that internal air velocity fields serve as a significant operational driver influencing the effective radon removal parameter. This localized hydrodynamic behaviour exerts a more profound influence on the overall operational loss rates than the structural aperture area alone, meaning that neglecting the potential effects of random factors, such as uncontrolled environmental conditions, could overlook operational variances. A notable difference was observed between the ventilation rate measurements based on tracer CO₂ gas decay method and those based on passive and active radon techniques. Applying an average ventilation rate of 0.00635 ± 0.00043 h^-1, as determined through active radon technique, effectively corrected measurements within the constructed chamber. Adjusting for ventilation effects improved calibration precision, reducing deviations from reference values to within 2%. These findings highlight the critical importance of incorporating ventilation rate adjustments in calibration and environmental radon measurements to ensure accuracy and reliability in radon metrology.