Determination of ²³¹Pa in coastal sediments and sea water and disequilibrium studies in ²³¹Pa/²³⁵U activity ratios

Abstract

Coastal sediment samples are collected from the top surface layers of the sediments from Bombay to Kottilppad along the West coast of India in order to understand the geochemical behaviour of ²³¹Pa and the activity ratios of ²³¹Pa/²³⁵U in this region of the Indian sub-continent. These coastal regions offer a unique advantage for studying the geochemistry and transport of natural radioactivity due to the placer deposits of monazite in the southern part of India. The top layers of the surface sediments are leached with 1.0M oxalic acid for the extraction of protactinium activities without attacking the mineral core of the particles. ²³³Pa tracer is added to the samples. The chemical recovery obtained by counting ²³³Pa is found to vary from 40 to 90%. Total uranium leached from the sediment surface is determined by fluorimetric method and the concentrations of ²³⁵U in the leachates are calculated. Using these data, the activity ratios of ²³¹Pa/²³⁵U have been calculated. These ratios lie in the range of 11.0 to 21.0 for sediments from Bombay to Kottilppad. The data of ²³¹Pa activity indicates that there is a deficiency of ²³¹Pa in coastal waters of the ocean and that ²³¹Pa is removed by precipitation as soon as it is formed by radioactive decay of ²³⁵U. ²³¹Pa is observed to be bound mostly to organic humous material on the surface of the sediment.