Determination of uranium by liquid scintillation and Cerenkov counting

Abstract

Three radiometric methods for the determination of uranium in aqueous samples, involving the use of a liquid scintillation counter, have been studied and compared. Uranium is separated and purified by coprecipitation with iron(III) hydroxide followed by an anion-exchange process. The purified uranium in the eluate (0.1 mol l^–1 HCl) can either be collected and stored and the Cerenkov radiation from the in-growth of the high-energy β-emitter ²³⁴Pa counted, or the uranium can be extracted from the chloride eluate into diethylhexylphosphoric acid in toluene containing appropriate scintillation materials and counted by a liquid scintillation technique. Alternatively, uranyl chloride can be converted into uranyl nitrate, which is then dissolved in 1 ml of 1,4-dioxan, and the solution is subsequently mixed with scintillation solution and counted. In the liquid scintillation methods, both ²³⁴U and ²³⁸U can be determined, but, by using the Cerenkov method, ²³⁸U is measurable in isolation. Several variants of the chemical-separation procedure have been studied in relation to their effect on quenching, sensitivity and accuracy. The background count rates observed were 0.04, 0.075 and 0.213 counts s^–1 for the 1,4-dioxan, extraction and Cerenkov techniques, respectively; the lower limit of detection was taken as 3σ of the background. Chemical yields were in the range 80–90%.