Neutron Activation Analysis of Thorium in Natural Waters

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Neutron activation analysis of thorium in mineral springs and coastal waters is reported. After preliminary concentration of thorium in natural waters with coprecipitation of ferric hydroxide, the samples were irradiated in JRR-2. The <SUP>233</SUP>Pa produced in the target materials was radiochemically separated by solvent extraction with DIBK-hydrochloric acid system, and the electrodeposited source was counted. The chemical yield was verified by <SUP>231</SUP>Pa tracer. The reliability of this method was ascertained by the use of standard rock G-1. Values of 0.01 to 0.5 μg/l were obtained for thorium content in waters from several springs in Japan. These values are very much lower than those previously reported, and the characteristics varying with region are reported. Some geochemical considerations with regard to the origin of uranium in the springs of such localities as Asanbara and Misasa are discussed.
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