Dispersion corrections to the forward Rayleigh scattering amplitudes around the L-shell of tantalum and lead

Abstract Dispersion corrections to the forward Rayleigh scattering amplitudes of tantalum and lead in the photon energy range 6.4–24.14 keV were determined by a numerical evaluation of the dispersion integral that relates them through the optical theorem to the photoelectric cross-sections. The photoelectric cross-sections were extracted by subtracting the coherent and incoherent scattering contribution from the measured total attenuation cross-section, using a high-resolution, high-purity germanium detector in a narrow-beam good geometry setup. The real part of the dispersion correction to which the relativistic corrections calculated by Kissel and Pratt (S-matrix approach) or Creagh and McAuley (multipole corrections) have been included are in better agreement with the available theoretical values than those values to which the relativistic corrections calculated by Cromer and Liberman (dipole corrections) are added. Copyright © 2006 John Wiley & Sons, Ltd