Coulomb correction effect in Delbrück scattering and atomic Rayleigh scattering of 1–4 MeV photons

Previous large-angle investigations of atomic Rayleigh and Delbrück scattering in the few MeV energy range have been extended to small scattering angles. Rayleigh predictions obtained by combining the second-order S matrix for inner shells with the modified form factor for outer shells are accurate to better than 3%. Tentative estimates of Coulomb correction terms for the Delbrück amplitudes are obtained from the experimental differential cross sections using (i) general properties of scattering amplitudes, (ii) information from pair production valid at small angles, and (iii) rather firm arguments concerning signs and relative magnitudes of the scattering amplitudes at large angles and assumptions about the relative magnitudes of the Coulomb correction amplitudes at intermediate energies.