Sodium and Magnesium Fluorescence Analysis—Part II: Application to Silicates

Abstract

Moderate counting rates, in excess of 400 cps at a signal/noise ratio of 18 on 3.5% NaaO in rocks, permit high-precision quantitative analysis for light elements in silicates. Special advantages of fluorescence analysis in the 10 A region, with adequate excitation provided by an aluminum target tube, will be described. These advantages include an ease of discrimination by excitation potential and by high dispersion using large 2d space crystals. Minor and simple modifications of the optic path combined with electronic discrimination make the method ideal for sodium and magnesium. Routine runs over periods of days have been made possible by a new technique of calibration involving computer corrections for systematic drift from any source. Repeated tests show that the total analytical error, including specimen preparation, closely approaches that of the counting statistics used, and that the drift corrections are complete. In granitic rod; analyses resulting precisions (standard deviation/mean) are 1% for 2-5% Na₂O and 2% for 0.25-1.0% MgO.