Minimizing 'glitches' in XAFS data: A model for glitch formation

Spikes in X-ray absorption data, which are referred to as 'glitches', occur at particular monochromator energies for which multiple diffractions are possible. Measurements of the X-ray beam profile show that large spatial variations of the flux in the vertical direction occur at energies close to a glitch. We develop a simple model of glitch formation in ratioed X-ray absorption data, that shows why glitches remain in the ratioed data for ideal conditions (ideal detectors and no harmonics) if the sample is nonuniform. The model describes experimental observations well, including the occurrence of both negative and positive lobes in a glitch. Some ramifications of the model are presented and some means to minimize the glitches are discussed. The advantages of using pixel array detectors are also briefly presented. (orig.)