Use of Soller slits to remove reference foil fluorescence from transmission spectra

Measurement of X-ray absorption spectroscopy (XAS) in transmission is the method of choice for strong or concentrated samples. In a typical XAS experiment above 5 keV the sample is placed between the first (I₀) and second (I₁) ion chambers and a standard foil is placed between the second (I₁) and third (I₂) ion chambers for simultaneous calibration of energy during sample analysis. However, some fluorescence from the foil may be registered in I₁, causing anomalies in the transmission signal of the sample, especially when the sample edge jump is relatively small. To remedy this, Soller slits were constructed and placed between the foil and I₁ to minimize back-fluorescence from the foil. A comparison of blank and standard samples, measured with or without Soller slits or under a worst-case scenario, demonstrates the advantages of Soller slits when analyzing weak signal samples via transmission XAS.