A method is presented for the quantitative determination of thorium in monazite by fluorescent X-ray speetrometry. Strontium is used as an internal standard, and sample preparation consists of mechanically blending the finelyground (325-mesh) sample with reagent grade strontium carbonate. The prepared sample blend is packed into a sample cup and irradiated at 50 kV and 27 mA. A lithium fluoride analyzing crystal is used, and the intensity of the Th Lα1 and Sr Kα peaks are scaled. Intensities are corrected fov background. Calibration is achieved with a single sample of monazite of known thorium content. National Bureau of Standards monazite sample number 2601 (9.65% ThO2) was used in this work. The standard monazite is blended with strontium carbonate, irradiated, and scaled under the same conditions as the sample. The thorium content of the sample is then calculated by the equation: %ThO2 = (R sample) (%ThO2 standard)/R standard, where R = Thcounts/sec/Srcounts/sec. Replicate results agreed within 0.2% ThO2 on six samples of monazite which contained from 4.4% to 6.8% ThO2. Independent results by a second laboratory show no significant difference in precision.

The method was used to determine the thorium content gf several rare-earth materials which contained approximately 0.5% to 1.0% TriOs. The results agree closely with values obtained by gamma-ray spectrometry.