Measurements of 222Rn in Air Using a Flow-Through Lucas Cell and Multiple Time Analysis of Recorded Pulse Events

A multiple time analysis technique has successfully been applied for measurements of environmental levels of 220Rn using a flow-through Lucas radon detector. The method is based on selective alpha counting of the short-lived nuclide 216Po. Owing to its short half-life (0.145 s), the alpha particle emitted at the decay of a 220Rn atom will, within a fraction of a second, be followed by an alpha particle from the decay of 216Po. By measuring the time interval between successive alpha counts followed by a multiple time analysis, the 216Po activity and thereby the 220Rn activity can be calculated. The method applied to a commercial instrument with a 160 ml Lucas cell as detector shows that a mean 220Rn air concentration of less than 20 Bq.m-3 can easily be determined even if the 22Rn air concentration is 10 times higher and varies. At lower 222Rn levels a 220Rn concentration less than 1 Bq.m-3 can be assessed using this technique. The method will be described together with some examples of its practical use.