On the techniques for primary calibration of electronic radon detectors

Successful calibration of RadonEye +2 electronic radon detectors was performed at typical indoor activity concentrations using the facilities at LNHB and PTB. The calibration uncertainties using primary radon activity standards were: below 1.5 % at 300 Bq/m³, below 1.7 % at 130 Bq/m³ and below 2.5 % at 55 Bq/m³ (k = 1). When using the secondary standard AlphaGUARD, the uncertainty at 55 Bq/m³ was below 3.5 %. Maintaining stable activity concentrations proved crucial and appears to be the only feasible approach for calibrations below 100 Bq/m³. While calibration under exponentially decaying radon activity concentration remains useful for evaluating the devices' linearity across a broad range, it proved unsuitable for calibration of user-grade monitors at low activities due to the high statistical variation in their signal. The linearity of RadonEye +2 was demonstrated in the range 50 Bq/m³ - 300 Bq/m³ and they will be utilized for the sensor networks developed within the RadonNET project. Dynamic background correction, applicable to non-spectrometric detectors, was applied based on the monitor's exposure history. Furthermore, it was observed that the pulse-processing algorithm of RadonEyes +2 distorts the Poisson distribution of the signal, thereby increasing its variation. Potentially, lower measurement uncertainty could be achieved with electronic radon detectors that report the registered pulses and allow access to their processing algorithms.