Evaluation of 222Rn and 220Rn discriminating concentration measurements with pinhole-based twin cup dosimeters using computational fluid dynamics simulations

Abstract Pinhole-based twin cup dosimeters are capable of distinguishing 222Rn and 220Rn passively, as well as measuring their concentrations via Solid State Nuclear Track Detector films. However, the reliability of the measurements can be affected by environmental conditions and design of the device. To evaluate the significance of diffusion coefficient of air, radius, length, and number of pinholes, as well as radius and length of the twin cups on the effectiveness of the device, computational fluid dynamics models were developed for 14 scenarios. Concentration distributions of 222Rn and 220Rn were obtained, with their transmission factors each calculated and compared for the twin cups and for the pinhole(s). The results suggest that little to no impact was made on 222Rn's transmission factors, despite the change in diffusion coefficient and dimensions of the pin hole and the twin cup. However, for 220Rn, transmission factors significantly increased with an increase in pinhole radius, number of holes, or diffusion coefficient, or a decrease in pinhole length, twin cup length, or twin cup radius.