Determination of²³¹Pa in coastal sediments and sea water and disequilibrium studies in²³¹Pa/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 of²³¹Pa and the activity ratios of²³¹Pa/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 counting²³³Pa is found to vary from 40 to 90%. Total uranium leached from the sediment surface is determined by fluorimetric method and the concentrations of²³⁵U in the leachates are calculated. Using these data, the activity ratios of²³¹Pa/²³⁵U have been calculated. These ratios lie in the range of 11.0 to 21.0 for sediments from Bombay to Kottilppad. The data of²³¹Pa activity indicates that there is a deficiency of²³¹Pa in coastal waters of the ocean and that²³¹Pa is removed by precipitation as soon as it is formed by radioactive decay of²³⁵U.²³¹Pa is observed to be bound mostly to organic humous material on the surface of the sediment.