RARE-EARTH ELEMENT DETERMINATION IN MINERALS BY ELECTRON-PROBE MICROANALYSIS - APPLICATION OF SPECTRUM SYNTHESIS

Electron-probe microanalysis (EPMA) is applicable to rare-earth elemen ts (REE) in minerals with relatively high REE concentrations (e.g. hun dreds of parts per million). However, given that each of the 14 REE ha s at least 12 X-ray lines in the L spectrum, finding peak-free regions for background measurement can be problematical. Also, measured peak intensities are liable to require correction for interferences. Hither to, little attention has been paid to the optimisation of background o ffsets and the implications of the wide variation in REE distribution patterns in different minerals. The 'Virtual WDS' program, which enabl es complex multi-element spectra to be synthesised, has been used to r efine the conditions used for different REE distributions. Choices inc lude whether to use the L beta(1) rather than the L alpha(1) line, bac kground offsets, and counting times for comparable relative precision. Correction factors for interferences affecting peak and background me asurements have also been derived.