1979 Volume 28 Issue 11 Pages 661-665
220Rn in mineral springs is easily extracted into toluene solution (containing a definite amount of liquid scintillator), which is carefuly transferred into counting vial. The activity in the solution is measured by integral counting technique with a liquid scintillation counter. 220Rn, being extracted, rapidly disappears but 212Pb (half-life 10.64 h) and its descendants form a radioactive equilibrium in toluene solution around 3.7 h after the extraction. The establishment of radioactive equilibrium is proved by α and β rays energy spectrum and also by the formation of growth decay curve. The shape of this curve entirely coincides with decay curve constructed by application of the Bateman equations for 212Pb and its descendants. It was proved that integral counting technique could practically give hundred percent counting efficiency for 1α and 2β emitters in radioactive equilibrium. A calculating formula for 220Rn contents in water is proposed based upon these facts, together with necessary correction terms such as extractability, decay rate during measurement and so on. The detection limits of this method is found as (6.8±0.9)×10-10 Ci (standard deviation in counting) under the conditions of 5 cpm (one tenth of background counting rate) and total counting time of 400min. Some practical examples of determination of 220Rn in mineral springs are shown together with 222Rn contents to prove the availability and feasibility of this method.
