Large Volume Radon Exposure System for Calibration and Studies of the Dynamic Characteristics of Radon Monitors

It is well-known that indoor radon exposure causes lung cancer. Up to now, radon risk estimation has relied on measurements by passive track detectors, because they allow long-term cumulative measurements at numerous points at low cost. A major drawback of passive detectors is the lack of real-time information about radon concentration and its dynamics. Recently, low-cost active radon monitors became commercially available. They have properties sufficient to follow radon dynamics even at low radon concentrations, typical for buildings with normal radon levels. This development opens up new applications, such as studies on radon dynamics and the factors influencing it, better estimation of the radon exposure, especially in buildings with part-time occupancy, and integration with “smart” buildings with smart radon mitigation systems. To ensure reliable measurements of the radon concentrations and dynamics, these new active monitors require sound metrological assurance. To address this need, a special exposure system was developed with a 200 l hermetic exposure volume, equipped with several inlet/outlet valves, a standard 220 V AC power supply, 3 standard USB-3 communication ports, two external pumps, a certified radon source and two reference radon monitors. In this work we demonstrate the capabilities of this system to provide constant reference radon concentrations in the range from 350 Bq/m³to 500 kBq/m3 suitable for calibration of both passive and active radon detectors. The system can also create slow-changing radon concentration suitable for studying the linearity as well as fast-changing concentrations suitable for studying the time response of active radon monitors. This dynamic regime also enables the reproduction of real/field exposure at predefined, controlled radon concentration.