Study on the dynamics of radon concentration buildup in the closed-loop measurement system with RAD7 online radon monitor.

The article focuses on developing and validating an alternate dynamical model for radon (^222Rn) and thoron (^220Rn) exhalation rate measurements in a closed-loop system using online radon monitors, specifically the RAD7. Unlike the conventional single-volume mass balance approach, the proposed model treats the sample chamber and detector chamber as separate entities connected by tubing, incorporating air flow rate and decay losses, which is particularly significant for short-lived thoron. Experimental results showed that radon buildup profiles are not affected by pump flow rates below the standard 1 L min^−1, and variations observed at lower flow rates are attributed to inadequate correction for thoron interference in the RAD7 measurement protocol. The model accurately simulates radon dynamics and confirms that thoron concentrations in the detector chamber are substantially lower than in the sample chamber due to decay during transit, aligning with RAD7 calibration factors and supporting the model’s validity for thoron measurement corrections.