Portable two-filter dual-flow-loop 222Rn detector: stand-alone monitor and calibration transfer device

Little overlap exists in the required capabilities of ²²²Rn (radon) monitors for public health and atmospheric research. The former requires robust, compact, easily transportable instruments to characterise daily to yearly variability >100 Bq m⁻³, whereas the latter requires static instruments capable of characterising sub-hourly variability between 0.1 and 100 Bq m⁻³. Consequently, detector development has evolved independently for the two research communities, and while many radon measurements are being made world-wide, the full potential of this measurement network can't be realised because not all results are comparable. Development of a monitor that satisfies the primary needs of both measurement communities, including a calibration traceable to the International System of Units (SI), would constitute an important step toward (i) increasing the availability of radon measurements to both research communities, and (ii) providing a means to harmonize and compare radon measurements across the existing eclectic global network of radon detectors. To this end, we describe a prototype detector built by the Australian Nuclear Science and Technology Organisation (ANSTO), in collaboration with the EMPIR 19ENV01 traceRadon Project and Physikalisch-Technische Bundesanstalt (PTB). This two-filter dual-flow-loop radon monitor can be transported in a standard vehicle, fits in a 19^′′ instrument rack, has a 30 min temporal resolution, and a detection limit of ∼0.14 Bq m⁻³. It is capable of continuous, long-term, low-maintenance, low-power, indoor or outdoor monitoring with a high sensitivity and an uncertainty of ∼15 % at 1 Bq m⁻³. Furthermore, we demonstrate the successful transfer of an SI traceable calibration from this portable monitor to a 1500 L two-filter radon monitor under field conditions.