X-Ray Fluorescence Analytical Techniques - CNSTN : Centre ...

homogenization of the analysed material which is most easily done by fusing the sample or
taking it into solution. Such a preparation of samples, however, makes the whole analysis
complicated and time consuming.
Figure IV.4: Schematic illustration of particle size effects.
The direction of the changes in the fluorescent intensity which follow given changes in
particle size depends on the ratio of the absorption coefficients for this fluorescent radiation of
the particles containing the excited element (fluorescent particles) and of the matrix particles.
For a rather weakly absorbing matrix, the fluorescent intensity decreases with the particles
size. In strongly absorbing matrices, this relationship is just the opposite (Figure IV.5).
Figure IV.5: Variation in the fluorescent X-ray intensities versus diameter of the sample
grains; 1- weak absorption of fluorescent radiation in light matrix, 2- strong
absorption of fluorescent radiation in matrix containing heavy elements.
II.4 Mineralogical Effects
These effects are caused by the influence, on the fluorescence intensity of the wanted
element, of the type of mineral in which this element occurs (Figure VI.6). These phenomena
have been reported by, among other, Campbell and Thatcher (1960) for fluorescence
determination of calcium in such samples as carbonate, tungstate, or phosphate. A similar
effect has been reported by Bernstein (1962, 1963) in the analysis of copper ores, where the
copper was in the form of chalcopyrite (CuFeS2) and connelite (CuS).