Customization of an in-house XAFS spectrometer for sulfur measurement

In-house XAFS spectrometers suitable for routine experiments are getting fairly popular today. One of the problems of such apparatus is the capability to study low atomic number materials. In general, elements with atomic number 20 (i.e. Ca) and below is difficult to measure because absorption of air becomes large. In this energy region, very important elements for environmental studies, such as S and P are involved. Either an evacuated or a He-filled X-ray path is required for getting enough photons in the low energy region. Since most in-house XAFS spectrometers apply Rowland Circle configuration, the spectrometer shows fairly complicated movement during energy scan. Varying the distance between the X-ray source and the bent crystal requires bellows for evacuating the X-ray path or substituting by He, but it restricts the spectrometer scanning range, especially on the low angle side. However, the low angle range (i.e. 30 to 60 degree) is most commonly used and X-rays are efficiently collected in this range. We have customized a commercial XAFS spectrometer to be capable for energies as low as 2 keV for sulfur measurement without sacrificing its scanning range.