Dispersion corrections to the forward Rayleigh scattering amplitudes of tantalum, mercury and lead derived using photon interaction cross sections

Dispersion corrections to the forward Rayleigh scattering amplitudes of tantalum, mercury and lead in the photon energy range 24–136 keV have been determined by a numerical evaluation of the dispersion integral that relates them through optical theorem to the photo effect cross sections. The photo effect cross sections have been extracted by subtracting the coherent and incoherent scattering contribution from the measured total attenuation cross section, using high-resolution high-purity germanium detector in a narrow beam good geometry set up. 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.