Improved In Situ Determination of Radon in Water Using a Degassing Membrane Tubing

Naturally occurring radioisotope radon (222Rn) is widely used as a tracer for investigating various geophysical processes in marine and aquatic environments. Its application often necessitates the acquisition of continuous radon activities data. Here, we introduce an improved approach for continuous measurement of radon in water by integrating an expanded polytetrafluoroethylene (ePTFE) membrane tubing with a pulsed ionization chamber (PIC) radon sensor. The detection limit of the system is 1.12 × 10–2 Bq in 400 min. Our proposed system achieves radon degassing efficiency comparable to the widely used RAD7-RAD AQUA system but has the advantage that its efficiency is less affected by humidity. The response time of the system is ∼1 h when using a 30 m length membrane tubing. Besides, the radon diffusion coefficient for our membrane tubing was 3.3 times that of the commercially coiled membrane tubing “water probe” under the same experimental condition. Continuous measurements were conducted and lasted for over one month in the laboratory, successfully capturing radon dynamics. This approach will be conducive to study several aquatic and hydrological processes such as long-term monitoring of groundwater fluxes in lakes, wells, and coastal seas.