Determination of thorium in monazite by X-ray fluorescence

X-ray fluorescence method was applied to the determination of thorium in monazite, and the addition method combined with the internal standard method (Sr as internal standard) was found suitable. Procedure:-After strontium carbonate (50 mg) and thorium oxide (0, 30, or 60 mg) are added to the monazite (500 mg), the mixture is fused with potassium hydrogen sulfate (5g). The fused matter is crashed to fine powders, and the intensities of Th Lα1-1 and Sr Kα1-1 of the three powdered samples thus prepared are measured. The content of thorium in each monazite was calculated either from the ratio ITh/ISr, or from ITh by applying the theoretical equation (1) or (2), respectively. The former gave results close to those by chemical analysis, while the latter gave a little higher ones. So far as the monazites used in this study are concerned, the intensities of Th Lα1-1 and of γ-rays emitted from the monazites themselves were both nearly proportional to the values obtained by the above procedure.