A new method for automatic measurement of low-level radon in water

A new single phototube liquid scintillation counting system for automatic determination of 222Rn in ground water for earthquake prediction is described. About 40% of radon is transferred from 1.0 L of water with a stream of air into 25 ml of toluene in a sample vial. Delayed coincidence counting of 214Bi and its decay product, 214Po reduces the background to 0.02 cpm. The 214Po detection efficiency is above 90%. Water containing 20 mBq/L of radon can be measured with 10% accuracy in 3 h.