Reducing the detection limit of the radon monitor with less humidity influence based on electrostatic collection...

Radon is the primary natural radiation source for humans, necessitating accurate concentration measurement for protection and assessment. High - precision instruments with low detection limits are crucial for outdoor low-concentration environments. This study improved the Hynu EIRM detector by addressing two key limitations: the large collection dead zone and the high detection limit, resulting in the optimized Hynu EIRM III with minimized humidity sensitivity. (1) Geometric factor: The hemispherical chamber's flat cover was redesigned to an inverted conical frustum with a recessed CR-39 mount flush with the chamber bottom. COMSOL simulations verify a relatively uniform electric field distribution, with the majority of field lines oriented toward the detector surface, which effectively reduces the collection dead zone. (2) Collection voltage: According to the defining equation, lowering the detection limit requires increasing the measurement time. Theoretical analysis showed <8 % collection efficiency difference between 1000 V and 2000 V. Therefore, the chamber voltage was lowered to 1000 V, then the measurement time was extended by 4 times. Experiments were conducted under three different relative humidity conditions. From low (RH < 20 %) to high (RH > 98%) humidity, the detection limit only increases by ∼10 %. The optimized detector achieved an average calibration factor of 0.0147 ± 0.0008 tracks·cm^-2(Bq·m^-3·h)^-1 and a detection limit of 5.02 ± 0.27 Bq·m^-3, representing a 24 % higher calibration efficiency and 76 % lower detection limit versus the original Hynu EIRM detector.