Effect of some important sample parameters on the X-ray fluorescence determination of impurities in pure materials: determination of Ca, Y, Gd and Th in uranium

Calibration standards obtained by dry mixing of the components in appropriate proportions may be compositionally accurate but they can be a major source of error in the x-ray fluorescence analytical results owing to the mismatch in the degree of their homogeneity with that of the sample. An in-depth study has been made on the above aspect taking U3O8 as a matrix and Ca, Y, Gd and Th in the low concentration range (0-1500 ppm) as representative impurities. This study clearly illustrates the incompatibility of the truly homogeneous standards with the standards obtained by dry mixing and grinding. This incompatibility is dependent on the analytical line wavelength, being large for soft x-ray lines and small for harder x-rays. The effect of binding material which is often required for briquetting the sample into a pellet form and is necessarily to be mixed with the sample by dry mixing is discussed. (author)