Determination of uranium by liquid scintillation and Cerenkov counting

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%.