Electret method for continuous measurement of the concentration of radon in water.

A passive system using an electret ion chamber to measure dissolved radon in a water sample has been recently described. In the current work, an electret ion chamber has been used to measure time-averaged concentration of dissolved radon in water. A steady concentration of radon in water is generated by bubbling radon gas into water in a 20-L jar and maintaining constant rates of feed and bleed of the water. To perform the measurement, the outgoing water flows into a 4-L cylindrical chamber. Air is bubbled at 1 L min-1 through a 10 cm long sintered stainless steel tube immersed in this water releasing the radon from water into the chamber volume. A 1-L electret ion chamber ("H" chamber) loaded with an electret is hung in the 4-L chamber. Radon diffuses into the "H" chamber through its tyvek (carbon-coated) covered openings. The radon concentration in air is measured from the change in electret voltage. The concentration of radon in water is then obtained from the concentration of radon in air and the air and water flow rates. For comparison, the radon concentration in water was measured using a standard liquid scintillation counting method. For the concentration range covered (4.7 to 72 Bq L-1), there was a good agreement between the two methods.