Measurements of x-ray atomic scattering factors of high-Zmetals

Abstract

The coherent scattering of 25- to 75-keV filtered fluorescence $K\ensuremath{\alpha}$ radiation from thin Sn, Sm, Ta, Pt, and Au foils has been measured absolutely. Values of atomic scattering factors in the range of $q=\frac{sin(\frac{\ensuremath{\theta}}{2})}{\ensuremath{\lambda}}$ from 0.5 to 5.5 ${\mathrm{\AA{}}}^{\ensuremath{-}1}$ were obtained for five different incident energies with scattering angles ranging from 45\ifmmode^\circ\else\textdegree\fi{} to 135\ifmmode^\circ\else\textdegree\fi{}. Our results are compared with Cromer's recent relativistic Dirac-Slater calculations with and without anomalous dispersion corrections. When plotted against the ratio of the target $K$-edge energy to the incident energy, differences between measured and calculated scattering factors follow the same general trend for all these high-$Z$ elements. Before they are corrected for dispersion, the calculated scattering factors for incident energies below the target $K$-absorption edge exceed the measured values, with the difference increasing in magnitude as the $K$ edge is approached. After the dispersion correction, the calculated values are all lower than the measured values by about 1.3 units. For incident energies above target $K$ edges, differences are generally small; but uncorrected calculated scattering factors also exceed the experimental values in a rapidly increasing manner as the $K$ edge is approached. After they are corrected for dispersion, calculated values are lower than measured values by about 0.6 units. Improved agreement can be obtained over the whole energy range for each element by arbitrarily reducing the magnitude of the real part of the dispersion correction term to that of the principal anomalous term.