Upgrade of a Highly Sensitive Monitor for Atmospheric Radon Measurement

Atmospheric radon is an ideal tracer that is widely used in atmospheric science. To meet the need fora continuous online measurement of atmospheric radon concentration, an upgraded radon monitor based on an electrostatic collection method was developed following Iida’s measurement system. Two major improvements have been realized. First, an 18 mm × 18 mm Si-PIN detector and a multi-channel analysis system were used to distinguish different alpha particles. Second, the P2O5 desiccant was replaced by a new membrane drying system, and the influence of humidity was corrected by a humidity correction coefficient. Calibration and comparison experiments were carried out in detail, and a one-year continuous measurement was also performed. Results showed that the measurement sensitivity was evaluated to be 24.3 cph/(Bq·m−3), and the lower level detection limit was 0.2 Bq·m−3 for a 1-h cycle at the absolute humidity of 0.34 g·m−3. The annual average radon concentration of Beijing was 11.1 ± 4.0 Bq·m−3, which changed from 2.8 Bq·m−3 to 30.3 Bq·m−3 between 15 October 2018 and 1 October 2019. The upgraded monitor’s high data acquisition rate and good performance indicate that it is suitable for long-term observation on atmospheric radon.