In-House Equipment and Synchrotron Radiation Facilities for Anomalous X-ray Scattering

Abstract

An energy lower than the absorption edge is usually selected in anomalous X-ray scattering (AXS) measurement, in order to avoid strong fluorescent radiation from a sample. In this energy region, the real part of the anomalous dispersion factor changes drastically, whereas the imaginary part and its energy variation are quite small. However, as long as only characteristic radiation produced from the sealed tube X-ray source is used, the change due to the anomalous dispersion effect is limited for a small number of elements (see Fig. 3.2) and is on the order of a few percent of the normal atomic scattering factor. This is because the energies of the characteristic radiation are not always close enough to the absorption edge for a desired element. Therefore, the AXS measurements are designated to vary the X-ray energy continuously by combining an appropriated crystal monochromator with white radiation, such as a tungsten or gold target with a rotating-anode-type X-ray generator, or a synchrotron-radiation source. In this way, by tuning the crystal monochromator, the anomalous dispersion can be maximized.