Secondary Fluorescence in WDS: The Role of Spectrometer Positioning

Area of Science:

• Analytical Chemistry
• Materials Science
• Geochemistry

Background:

• Secondary fluorescence (SF) is often a minor error in electron probe microanalysis (EPMA).
• SF can become significant in high-precision trace element analyses of multiphase samples.
• Wavelength dispersive spectrometer defocusing can also introduce analytical artifacts.

Purpose of the Study:

• To investigate the impact of secondary fluorescence and spectrometer defocusing on EPMA trace element analysis.
• To evaluate the accuracy of modeling codes (PENEPMA, FANAL) in correcting these errors.
• To determine the dominant source of systematic error in trace element quantification.

Main Methods:

• EPMA transects were performed across two material couples with high fluorescence yields.
• Measurements were taken at varying distances and orientations relative to the fluorescent phase and spectrometer focal line.
• Results were compared with calculations from Monte Carlo (PENEPMA) and semi-analytical (FANAL) models.

Main Results:

• Both PENEPMA and FANAL can estimate SF magnitude, but accurate correction depends on spectrometer position.
• Apparent SF yield varied by a factor of 1.2-1.8 based on spectrometer positioning over the fluorescent phase.
• Secondary fluorescence was the dominant error, causing 0.1 wt% apparent Zn in Al, with ~200 ppm attributed to spectrometer defocusing.

Conclusions:

• Secondary fluorescence and spectrometer defocusing introduce systematic errors in trace element EPMA.
• Accurate modeling of SF requires precise knowledge of spectrometer position.
• SF is the primary error source, necessitating careful consideration in high-precision analyses.