X-ray absorption fine structure spectrometer using a compact superconducting synchrotron radiation source

Abstract

We have constructed an x-ray absorption fine structure (XAFS) spectrometer at BL-4 using the compact superconducting synchrotron radiation (SR) source at Ritsumeikan University. BL-4 is simply designed and consists of a slit, a double-crystal monochromator, and two detectors. The mechanical movement of the monochromator is in the range from 15° to 75°. By using Si(220), Ge(220), and InSb(111) crystals, the XAFS spectrometer covers the K-edge absorption energies of elements from silicon to zinc under atmospheric pressure. The incident x-ray intensity is measured by an ionization chamber with a path length of 4.5 cm. The transmitted x-ray intensity after passing through a sample is monitored by either an ionization chamber with a path length of 31 cm or a scintillation counter. The steep decrease of x-ray intensities above 5 keV is characteristic of the spectrum of photons emitted from the compact SR source and the photon flux at 10 keV is two to three orders of magnitude smaller than that at 5 keV. Hence, the contamination of higher-order harmonics is negligible above 5 keV. The double-crystal monochromator should be detuned only in measuring K-edge XAFS spectra of K, Ca, and Sc by using Si(220) or Ge(220). Suitable gases for two ionization chambers are easily selected only based on the detection efficiency of He(100%), N2(100%), N2(85%)+Ar(15%), N2(50%)+Ar(50%), and Ar(100%) gases. The photon flux passing through a 2 mm×9 mm aperture is estimated from the ion current of the ionization chamber. Though the values normalized to 1 mm2 are a few orders of magnitude smaller than those of BL7C at the Photon Factory, it turned out that measurements of XAFS spectra of good quality are very easy to obtain from 1.7 to 10.5 keV by using the spectrometer at BL-4.