Determination of 222Rn and 226Ra in water using a large volume ionisation chamber

A new method for measuring 222Rn and 226Ra in water has been devised. It is based on exhaling radon to a void volume by continuous bubbling of air through the water. The exhaled radon is then transferred in a closed circuit to a modified radon gas pulse ionisation chamber for alpha-spectrometric measurements. About 86% of the radon in water is transferred from 0.75 l of water to the void volume (3.2 l). The set-up offers direct and specific 222Rn measurements for a wide range of concentrations and shows a low detection limit (LLD=45 mBq l−1 for 8 h counting time). Radium in water is measured, via radon, after sample storage for a month. The method was compared with gamma ray spectrometry for radon and for radium, the latter after pre-concentration by co-precipitation with MnO2 from 10 l water samples. An excellent agreement between the two techniques was obtained. As a part of a radon survey, the method was employed for analysis of drinking water from bedrock wells.