Direct measurements of the complex X-ray atomic scattering factors for elements by X-ray interferometry at the Daresbury Synchrotron Radiation Source

A scanning X-ray interferometer system [Hart & Siddons (1981). Proc. R. Soc. London Ser. A, 376, 465-482] has been rebuilt for operation at the SERC Daresbury Synchrotron Radiation Source (SRS). The SRS permits an increase in energy resolution by one decade and simultaneously an intensity gain of one thousand times, though in practice the solid-state detector employed limited the peak intensity utilized so that experiments which hitherto demanded one month of counting time are now performed at higher spectral resolution in 2-4 h. Absolute measurements are reported of f' and f” for the K edges of most elements between ³⁴Se and ²⁶Fe and for L edges of ⁷⁹Au and ⁷⁴W over energy ranges of about ± 2 keV near absorption edges and scans with better than 1 eV energy resolution of X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra near the edges. Over wide energy ranges the results are compared with the most recent calculations of Cromer & Liberman [Acta Cryst. (1981), A37, 267-268], which are now easily available to workers in the field.