INSTRUMENTATION FOR TXRF AND GI-XRF - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 174

Figure3.20. Wavelength-dispersive spectrometer with flat crystal and gas-filled detector. The
centimeter-wide sample is excited to X-ray fluorescence at total reflection or under grazing
incidence by the primary X-ray source. The secondary radiation of the sample is directed to the
Bragg crystal by a first collimator and reflected under an angle α according to Bragg'slaw.The
reflected monochromatic radiation is guided by a second collimator and reaches the detector
under an angle 2 α . The complete spectrum or a part of it is recorded if the Bragg crystal rotates
around its center on a vertical axis and the second collimator plus detector rotates with double
angular speed.

surface and vertical to the fluorescence beam, while the detector is turned
simultaneously around this axis at a double angular speed. This speed can be
chosen between slow (0.1 ° /min) and fast (180 ° /min). Crystal and detector have
to be adjusted with a precision of 0.01 ° .
In order to present the spectrum as dependent on the photon energy,
Bragg's law must be rewritten:

m hc 0
2 d sin α

E (3.19)