Increased radon detection sensitivity: extraction from 200 ml of water and liquid scintillation counting.

To increase detection sensitivity in a radon ground-water monitoring program, radon is extracted and transferred from 200 mL of water to a liquid scintillator by bubbling and circulating air through the two liquids in a closed system using a peristaltic pump. This results in a count rate that is 11 times higher than for samples prepared by the most widely used method, where 10 mL of water are added to 10 mL of scintillator. Preparation of counting samples is simple and takes 4 min. Standard deviation in radon concentration is 5% and minimum detectable activity is 5 mBq L(-1), using a counter with a background of 3 counts per hour and a counting time of 3 h. This method is also suitable for the measurement of radium in water.