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

A new method for measuring Rn-222 and Ra-226 in water has been devised. It is based on exhaling radon to a void volume by continuous bubbling of air t hrough the water. The exhaled radon is then transferred in a closed circuit to a modified radon gas pulse ionisation chamber for alpha-spectrometric m easurements. 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 Rn- 222 measurements for a wide range of concentrations and shows a low detecti on limit (LLD = 45 mBq l(-1) for 8 h counting time). Radium in water is mea sured, 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 101 water samples. An exc ellent agreement between the two techniques was obtained. As a part of a ra don survey, the method was employed for analysis of drinking water from bed rock wells. (C) 1999 Elsevier Science Ltd. All rights reserved.