In situ determination of the isotope sr-90 in the ground

Until now, in situ soil contamination could only be determined using methods which detect γ radiation from nuclides. Nuclides which only emit β radiation, such as 90Sr and the related 90Y, can however only be determined quantitatively in the laboratory. An overall assessment of soil contamination in vast areas caused by the 90Sr nuclide as the result of nuclear accidents or atomic bomb tests is an almost impossible task. In situ measurement could solve this problem. Interference is caused by the nuclides 137Cs and 40K which emit β and γ radiation. Other nuclides do not need to be considered due to their low half-life values. For in situ measurements, the combination of a scintillation detector and a methane continuous flow counter has been found to give optimal results. With the help of a subsequent anti-coincidence circuit both types of radiation can be separated and the measured nuclides can be quantified. The method has been shown to be suitable for in situ measurement. 90Sr at a concentration above 100Bq/kg with a measurement time of 1000 s can be detected. Improvement can be achieved in the γ spectrometrical field with the evaluation of potassium. The uncertainty in the detection and determination of potassium contributes to the larger part of the error associated with the analysis. (orig.)