Radon detection - RAD7
Radon-222 is an radioactive gas which is an excellent tracer of groundwater discharging to surface water bodies. Radon accumulates in groundwater due to radioactive decay of uranium and radium in aquifer materials and concentrations in groundwater are typically 1-2 orders of magnitude larger than surface water bodies, where radon is lost due to air-water exchange and radioactive decay.
In terrestrial hydraulic systems, radon is typically discretely sampled and analyzed using liquid scintillation methods. Instead a continuous, real-time, in situ radon gas detector can be used to analyze for radon-in-water concentrations. These methods have been recently developed by the oceanographic and hydrologic community [Burnett, et al., 2001; Burnett, et al., 2006; Kluge et al. 2007].
A commercial radon-in-air detector (RAD7) is outfitted with an air-water exchanger, called RAD-Aqua. Surface water is pumped continuously into the air-water exchanger and the concentration of 222Rn-in-air (which equilibrated with the surface water) is calculated by measurement of the daughters 214Po and 218Po. Radon-in-water concentrations are calculated from radon-in-air concentrations using the temperature dependence of the air-water phase equilibrium of radon [Burnett, et al., 2001]. Radon concentrations are measured over 10 minute intervals with an uncertainty of 0.02 Bq/L. Alternatively, radon-in-water concentrations can be measured using discrete samples in either the RAD-H20 or Rad-Aqua Plus.