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Wavelength Dispersive Microanalysis
Introduction
Electron probe X-ray microanalysis techniques (Wavelength Dispersive X-ray
and Energy Dispersive X-ray Spectrometries WDS and EDS, respectively) use
the characteristic X-rays generated from a sample bombarded with electrons
to identify the elemental constituents comprising the sample. Both
techniques generate a spectrum in which the peaks correspond to specific
X-ray lines and the elements can be easily identified. Quantitative data can
also be obtained by comparing peak heights or areas in the unknown with a
standard material.
Of the two methods, EDS is more commonly employed. Data collection and
analysis with EDS is a relatively quick and simple process because the
complete spectrum of energies is acquired simultaneously. Using WDS, the
spectrum is acquired sequentially as the full wavelength range is scanned.
Although it takes longer to acquire a full spectrum, the WD technique has
much improved resolution compared to EDS. Typical resolution of an ED
detector is 70 to 130 eV (depending on the element), whereas peak widths in
WD are 2 to 20 eV. The combination of better resolution and the ability to
deal with higher count rates allows WDS to detect elements at typically an
order of magnitude lower concentration than EDS.
While the WDS technique has always been appreciated for its higher
resolution and trace element capability, it has been traditionally viewed as
more complex to set up, and WDS data more tedious to obtain and interpret
than EDS.
And, in the past, it was.
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