THE USE OF SYNCHROTRON X-RAYS TO EXPLOIT THE WARREN-MAVEL FLUORESCENCE DETECTION TECHNIQUE IN STUDIES OF DISORDERED-SYSTEMS

Although the early structural studies of liquids and amorphous systems used x-ray diffraction, the advent of high flux reactor sources led to neutron diffraction becoming the preferred technique. There are several advantages: high scattering vector information is not form factor limited and, where isotopes exist, the variation in scattering length allows more detailed structural information to be extracted in many cases. However, the development of synchrotron radiation sources has generated renewed interest in x-ray measurements. High intensity is available at wavelengths short enough to give reasonable access to the high scattering vector region and, in theory, the tunability can be used to maximize anomalous scattering effects and so allow element specific scattering to be recorded. Another use of the tunability is for largely removing the Compton scattering which can often dominate the total scattered intensity and which contains no structural information. This technique requires a choice of incident photon energy such that the x rays scattered without energy loss excite fluorescence in a metal foil in the detection system while most of the Compton scattering has insufficient energy to do so. Hence, recording the fluorescence intensity effectively gives a measurement of the elastic scattering only. Whereas early experiments were limited by the available x-ray emission lines of conventional sources, synchrotron radiation can be tuned so that the incident energy is much closer to the absorption edge of the metal foil thus maximizing the efficiency of the technique. We demonstrate the power of this method and suggest where its application may continue to develop interest in x-ray experiments.