The determination of parts per million levels of thorium in optical components by x-ray fluorescence

A nondestructive technique for the determination of thorium in optical glass has been devised using tube-excited x-ray fluorescence with an energy-dispersive detector. Capability for full calibration and sample analysis has been incorporated into a computer-coupled system. Bulk thorium concentrations as low as 87 ppm have been detected with a coefficient of variation of 27.2% at 95% confidence using NBS-certified standards. At 466 ppm the coefficient of variation was 5.6% at the 95% confidence level. Qualitative determination of thorium in optical coatings has been demonstrated also.