Electron Probe Microanalyzer (EPMA) is a well-established analytical instrument for micro or submicron order element analysis of solid materials by detecting characteristic X-rays. In EPMA, X-rays are mainly measured by Wavelength Dispersive Spectrometer (WDS). WDS detects diffracted X-rays at a specific wavelength by adjusting the geometrical position of an analyzing device and an X-ray detector. Since WDS has a better energy resolution than Energy Dispersive Spectrometer, accurate quantitative maps can be obtained with WDS.
On the other hand, the drawback of the WDS quantitative mapping is the long analysis time. In the quantification process, the background intensity is subtracted from the peak intensity for each characteristic X-ray. Traditionally, the background intensity is estimated by the interpolation from measured X-ray intensities at off-peak positions. Since parallel detection of on-peak and off-peak X-rays is impossible with WDS, the off-peak intensity has to be measured separately, which increases the total measurement time for quantitative by a factor of 2 or 3 from the peak intensity measurement.
There is an alternative method to estimate the background intensity for WDS. The main source of the background is the continuum X-rays from the bremsstrahlung radiation, and the yield of continuum X-rays is known to be proportional to the mean atomic number (MAN) of the sample [ 1]. By calibrating the relation between the background intensity and MAN with a standard sample, the pseudo-background intensity for an unknown sample can be calculated by estimating the MAN and absorption effect in the matrix [ 2]. In this method, only peak intensity maps of the constituent elements are needed and off-peak measurements are not required, which reduces the total analysis time for quantitative mapping by that amount.
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