Nafion tube-based technology for extending desiccant longevity in RAD7 radon monitors

The RAD7 radon/thoron monitor is highly sensitive to humidity, causing traditional indicating desiccants to rapidly saturate and irreversibly degrade in field conditions. To address this bottleneck, this study innovatively introduces Nafion tubes as a passive pre-dehumidification unit within a closed-loop measurement system. Experiments were conducted in a constant-humidity chamber to evaluate the system using severely degraded desiccants. The results demonstrate that the baseline group, relying solely on degraded desiccant, maintained an effective measurement duration of only 3 h. In contrast, incorporating 1.2 m and 3.6 m Nafion tubes extended the effective operating times to 11.5 h and 27.5 h, achieving approximate 4-fold and 9-fold improvements, respectively. Furthermore, thermodynamic monitoring revealed that the Nafion membrane effectively recycled moisture, stabilizing the return-gas relative humidity at 35% and 67%, respectively. This low-cost, power-free strategy not only mitigates frequent desiccant replacement but also provides critical environmental buffering, establishing a highly stable thermodynamic microenvironment for continuous long-term monitoring.