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II. Energy Dispersive or Angle Dispersive?


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Energy Dispersive or Angle Dispersive?

The DAC was originally used in the so-called angle dispersive diffraction (ADD) mode in which Bragg's Law, λ = 2d sinθ, is fulfilled by using a fixed X-ray wavelength, λ, and scanning in angle, θ: this mode has already been discussed many times in the course. When intense near-parallel synchrotron X-rays became so readily available during the 1980's, many DAC practitioners turned to an energy dispersive diffraction (EDD) mode, in which the diffraction angle, θ, is fixed and rather Bragg's Law is fulfilled by measuring the diffracting photon's wavelength using an energy-dispersive detector: this mode has also been already discussed, in the Synchrotron section. The reasons for this switch were obvious:

However the advent in the 1990's of the image plate detector changed this perspective (image plates were discussed in the Synchrotron section, and again later in the Detectors part of this section) and we have witnessed a return to the ADD-mode of operation of DACs. The basic differences of such operation are illustrated below:


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© Copyright 1997-2006.  Birkbeck College, University of London.
 
 
Author(s): Paul Barnes
Simon Jacques
Martin Vickers