Anomalous behaviour of radio-isotopes of thorium in the coastal surface sediments of the Arabian Sea

L.U. Joshi, S.Z. Qasim

Abstract



Geochemical behaviour of Thorium isotopes and their activity ratios have been studied in the surface layers of coastal sediments collected from the Arabian Sea. These coastal areas offer an unique advantage for geochemical study and transport of natural radioactivity which can be correlated with the transport and deposition of artificially introduced radioisotopes or terrestrial run offs as pollutants in these areas. It is known that Southern region of the west coast of India is concentrated with large amounts of placer deposits containing thorium while the northern region is relatively free from such deposits. The surface layers of the coastal sediments are leached with 5% ethylene diamine tetra-acetic (EDTA) for the extraction of Thorium isotopes. The leaching agent is so chosen that it has a high efficiency for leaching thorium and at the same time it does not attack the core of the sediment particles. The Th228/Th232 activity ratios in the Kerala belt (8 degrees -77 degrees E) have been found to be in the range of 0.65 to 0.67, while this ratio is in the range of 2.00 to 2.18 in the northern region (19 degrees -13 degrees E, 73 degrees -75 degrees E). The Th230 and Th232 activities also show anomalous behaviour in these areas. The Th230 /Th232 activity ratio lies in the range of 0.95 to 1.07

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