Corrections for Na-loss on micro-analysis of glasses by electron probe X-ray micro analyzer

Abstract

The time-dependent loss of NaK_α X-ray intensity during the electron-probe micro analyzer (EPMA) analysis has become a serious problem in determining the chemical compositions of glass samples. An empirical method of correcting the Na-loss have been developed on the basis of observing decay curves of X-ray’s intensity and estimating the true Na intensities at 0s by EPMA.
However, the Na X-ray raw counts cannot be obtained from the monitor mode of our EPMA. In this study, we measured the time dependent decay profile by a line scan mode as a digital data without moving analytical spot for 20s with focused beam (5 μm analysis). Our method makes possible to evaluate the heterogeneity of Na concentration within a few μm scales and is suitable for the measurement such as vesicle-bearing and/or microlite rich samples. The corrected values by the present method are in good agreement with the chemical compositions determined by the defocused beam mode (30 μm analysis), which is not affected by Na-loss. Similar approaches to this method would be useful for the analysis of glass inclusion with narrow area.