Radium content and the activity ratio in groundwater from bedrock |
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| Authors: | Matti Asikainen |
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| Institution: | Institute of Radiation Protection, P.O. Box 268, SF 00101 Helsinki 10, Finland |
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| Abstract: | The relative abundance of 226Ra and 228Ra were determined in the groundwater from 125 drilled wells containing from < 0.1 to 51.3 pCi/l of 226Ra. The determination of 228Ra was carried out with a liquid scintillation counter by measuring only the weakly energetic β particles emitted from 228Ra. Thus the interference from the daughter nuclides of 226Ra was avoided, without specific separation of 228Ac. The direct measurement of 228Ra made the method decisively simpler and faster in terms of the chemistry involved.The concentration of 228Ra was found to be independent of the amount of 226Ra present in the samples. The concentrations of 228Ra were nearly the same over the whole range of 226Ra concentrations and the average ratio sharply increased as the 226Ra content of water increased. The ratio in the drilled wells varied from 0.3 to 26. Abnormally high ratios were found in areas with known uranium deposits as well as in several drilled wells at other locations. The abnormally high ratios present in groundwater suggest that the radioactivity anomaly is caused by uranium deposits and not by common rocks. In samples with a low radioactivity level the average ratio was slightly below unity, corresponding to the typical U/Th ratio of granite, the most common kind of rock in the study area. The samples from the rapakivi area proved to be exceptional in that they had a low ratio independent of the concentration of 226Ra. |
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