Development of a highly sensitive radon-222 amplifier (HiSRA) for low-level atmospheric measurements

Radon (²²²Rn), a radioactive gas with a half-life of 3.82 days, is continuously emanated from soil, rocks, and water by the radioactive decay of ²²⁶Ra. Radon-222 is released from the ground into the atmosphere, where it is transported mainly by turbulent diffusion or convection. For precise measurement of radon-222 atoms in the atmosphere, the detectors typically used present a small volume or surface area and are therefore not very sensitive, especially for online measurements and short sample intervals (<1 h). This article deals with the development of a Highly Sensitive Radon Amplifier (HiSRA) consisting in an enrichment system placed prior to a classic radon-222 analyzer. This system uses permeation membranes that make it possible to treat large quantities of air online (30 m³ h^-1). The radon-222 concentration is increased instantaneously by at least a factor of 30 across the HiSRA system. Therefore, in this study, when coupling to an ionization chamber (AlphaGUARDTM) at the outlet of the HiSRA system, the detection limit of the overall system is multiplied by factor of 30 and induces a new LD for a radon 222 gas analyzer lower than 1 Bq m^-3 for an integrating time of 10 min and 0.1 Bq m^-3 for 1 h. We constructed one radon amplifier prototype that provided the preliminary results for amplification efficiency and the initial measurements presented herein.