The significance of fluorescence in transmission X-ray absorption spectroscopy and X-ray absorption fine structure

We present a method to explore the effect of fluorescence on X-ray attenuation measurements obtained from X-ray absorption spectroscopy (XAS). We use the X-ray extended range technique-like method (XERT-like). The experimental setup includes different sized apertures to control the number of secondary X-rays entering the detector. Comparison of attenuation measurements produced with different aperture combination permit investigation of the effect of fluorescence radiation. In this work, fluorescence has a large impact on the attenuation measurements of thick zinc foils. The correction is energy-dependent and sample thickness-dependent and changes the structure and relative amplitudes of oscillations in the near-edge region. Correction for this systematic is important for absolute measurement, for edge-jump and edge characterization, and for near-edge structure and amplitudes. A significant background scattering due to zinc fluorescence from the beamline optics was identified and treated for the first time. The model theory fits the experimental measurements well. The resulting correction is most significant for thicker foils with the 50 mu m sample experiencing a shift in attenuation of up to 15.5% for the largest aperture while the 25 and 10 mu m samples saw corrections of up to 0.153 and 0.00639% respectively. The standard error from the dispersion and variance was reduced by up to 50.5% after the correction for the 50 mu m sample. This enables high-accuracy data and theoretical and experimental analysis to below 0.03% accuracy. The technology is advanced. There is a cost in preparation and measurement time of less than a factor of two, and the principles are clear and can be routinely implemented on any beamline. This paper focuses on the model and parameters for fluorescence.