Large-Angle Elastic Scattering of 1.33-MeV Photons from Lead and Uranium

The differential cross sections for the elastic scattering of 1.33-MeV photons from lead and uranium have been remeasured at angles ranging from 60° to 135°, using a lithium-drifted germanium detector. Dispersion relations are used to fix the relative phases among nuclear Thomson, Rayleigh, and Delbrück scattering. These relative phases and the calculations of the amplitudes for the individual scattering processes permit the theoretical cross sections to be determined. A discrepancy exists between the theoretical calculations and the experimental results. Previous suggestions for removing this discrepancy include incoherence between scattering from the nucleus and from the electrons, and a 180° phase shift between the parallel-polarization components of the nuclear Thomson and Rayleigh amplitudes. These suggestions are discussed and another possibility, destructive interference at large angles between Rayleigh scattering from the $K$ shell and from the $L$ shell, is presented.