An inexpensive and continuous radon progeny detector for indoor air-quality monitoring

A silicon photodiode-based inexpensive detector working as a counter and spectrometer for alpha particles has been conceived, designed, constructed and analyzed in depth. Monte Carlo simulations by means of MCNPX ver. 2.7.0 code have been carried out to select the most suitable sensitive element for the intended applications. The detecting unit has been coupled to an Arduino board and tested for low-rate alpha-particle counting and spectroscopy. Results demonstrate a maximum count rate of 4000 s-1, an energy resolution corresponding to a full width at half maximum of 160 keV over the entire energy range of measured alpha (namely 4 ÷ 6.5 MeV), and the sensitive element’s intrinsic efficiency of about 100%. Being the detector capable of distinguishing alpha energy associated to decays of radon daughters, its applications include 222Rn progeny monitoring. The air sampling system has been realized by a volumetric micro-pump forcing the air-flow through a millipore filter. By knowing the air-flow rate processed and the corresponding alpha energy spectrum measured, the concentrations of 218Po, 214Po and 210Po are determined. The potential alpha energy concentration-in-air is inferred, and effective dose evaluated. Calibration and testing measurements have been carried out by comparing the obtained results to the outputs of professional and expensive radon progeny monitor. The detector capability of “following” radon progeny concentration-in-air vs. time has been demonstrated. The device studied here can be configured as a prototype for an inexpensive radon progeny sensor to be potentially suitable for indoor air-monitoring in residential buildings, evaluating people’s exposures to radon and initiating corrective actions (e.g., mechanical ventilation) if necessary.