WDS
(Wavelength Dispersive Spectroscopy)
Wavelength dispersive spectroscopy is what gives the electron microprobe its analytical power. In wavelength dispersive spectroscopy, the wave properties of x-rays are used to identify and quantify the concentrations of the elements present in a sample by making us of the Bragg equation:
nλ = 2dsinØ
where
n= the order of diffraction (1,2,3...)
λ = x-ray wavelength
d = interplaner d-spacing of diffracting crystal
Ø = angle of incidence of x-ray on diffracting crystal
X-rays leave the sample in all directions and at all angles, but only those X-rays leaving the sample at 40 degrees (the Take Off Angle) can enter the wavelength spectrometer.
Inside the spectrometer is a diffracting crystal with a constant and known interplaner d-spacing (d). For a particular angle of incidence (Ø) only the X-ray wavelength (λ) that satisfies the Bragg equation will be diffracted to the detector.
Because the angle at which the x-rays strike the defracting crystal determines which element's x-rays will be defracted to the detector, changing the angle of incidence changes the element detected.
