A rapid beta gamma coincidence technique for determination of natural radionuclides in marine deposits

Abstract

A non-destructive and specific counting technique employing β and γ detectors in coincidence is described. The application of the present system rests on the fact that several daughter nuclides of ²³⁰Th and ²³²Th exhibit a favourable β-γ decay allowing their high sensitivity assay. It is experimentally demonstrated that the activities due to the radionuclides ²¹⁴Pb,²¹⁴Bi (²³⁸U series) and ²²⁸Ac, ²⁰⁸Tl (²³²Th series) can be unambiguously identified and measured without any chemical separation. The activity ratios ²¹⁴Pb/²²⁸Ac, ²¹⁴Bi/²²⁸Ac and ²¹⁴Bi/²⁰⁸Tl independently form a direct measure of ²³⁰Th/²³²Th in a geochemically closed system for radium isotopes. Thus, for deep sea sediments, manganese nodules, and other geochemical accumulations the present technique offers a quick and convenient method for measurement of ²³⁸U and ²³²Th daughter products, eliminating laborious chemical processing. In non-equilibrium systems such as sea water, after simple chemical preconcentration steps, the present method allows determination of the geochemically important activity ratio ²²⁸Ra/²²⁶Ra without introducing errors due to uncertainties in counting and chemical efficiencies. Results of measurements made using the β -γ assaying technique on a variety of marine sediments and nodules collected from the Indian and Pacific oceans and sea-water radium concentrates from the Arabian Sea are presented.