Effects of Ventilation and Forced Air Movement on the Activity Concentration of <sup>222</sup>Rn and <sup>220</sup>Rn

Background: Radon (<sup>222</sup>Rn) and thoron (<sup>220</sup>Rn) are naturally occurring radioactive gases with significant differences in half-life, influencing their indoor behavior. Radon has well-documented health risks and mitigation strategies, but thoron has received less attention. This study explores thoron behavior in relation to air flow dynamics and ventilation conditions used to mitigate radon levels.Materials and Methods: Controlled experiments were conducted from February to June 2021 in an empty basement room and a laboratory simulation. Radon and thoron activity concentrations were measured using Durridge RAD7 radon monitors. Forced air movement was achieved through a fan, and ventilation conditions were simulated in the laboratory using air pumps with inline flow control valves. The exhaust state varied between closed and open air systems.Results and Discussion: The experiments revealed that while radon concentrations were stable or decreased under both forced air movement and increased ventilation rates, thoron concentrations displayed an inverse relationship with forced air movement, irrespective of an open or closed air system. Additionally, thoron required much higher ventilation rates (>50 air changes per hour [ACPH]) to reduce concentration levels that radon achieved with much lower rates (1–10 ACPH). This suggests certain ventilation strategies might inadvertently elevate thoron levels despite reducing radon levels, indicating a nuanced interaction between thoron concentration and air flow dynamics.Conclusion: This study underscores the importance of considering thoron’s unique behavior when implementing ventilation strategies for indoor radioactive gas mitigation. It calls for a nuanced approach to managing air flow dynamics to effectively reduce both radon and thoron levels. Further research is needed to refine models for ventilation strategies in radiation hazard mitigation for radon and thoron.