Abstract
X-ray fluorescence methods have been used for determining molybdenum, niobium, thorium, tungsten, yttrium and zirconium as impurities or alloying constituents in tantalum and binary tantalum alloys being investigated as container materials for molten plutonium fuels. Various solvents were tested for dissolving tantalum samples, and hydrofluoric acid was found to be the most suitable. Samples are dissolved in hydrofluoric acid and diluted to a known volume; then the solution is analyzed by means of an X-ray tube with a tungsten target. X-ray tube operating conditions and counting times were selected to give good precision in a minimum time. Effects of impurities and variations in X-ray tube voltage and current, scintillation counter voltage, solvent composition, dilution volume and count rate were determined.Molybdenum, niobium and zirconium as impurities in tantalum within the concentration range of 25–2000 p.p.m. are determined by means of a line-to-background intensity-ratio method with a precision ranging from 17 p.p.m. at the 25–100 p.p.m. level to 43 p.p.m. at the 2000 p.p.m. level. From 0.5 to 10 per cent of tungsten in tantalum-tungsten alloys is determined with an absolute standard deviation of 0.09 per cent by comparing the intensity ratio of the tungsten Lα1 to tungsten LαCompton for the sample with ratios obtained for known standards. Thorium or yttrium in binary alloys is determined in the 0.025 to 10 per cent concentration range, using an internal standard procedure. Thorium is added as an internal standard in the determination of yttrium, and yttrium is added as an internal standard in the determination of thorium. Following sample dissolution, the ThF4, and YF3 precipitates are separated from the tantalum, dissolved in H2SO4and diluted to volume, and the intensity ratio of the thorium to yttrium lines is measured. Relative standard deviations of 7 and 2 per cent, respectively, were obtained in the 0.025–0.1 and 0.1–10 per cent concentration ranges for yttrium, and 12 and 3 per cent for thorium in the 0.025–0.1 and 0.1–10 per cent concentration ranges.
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