Elastic scattering of photons

Photon scattering from bound electrons of atoms, a component of the elastic photon-atom scattering amplitude called Rayleigh scattering, is discussed. General features of the many-body scattering amplitude and its partitionin g into Rayleigh and Delbruck land nuclear) single-electron transition scatt ering amplitudes are examined. The use of the state-of-the-art precise seco nd-order S-matrix calculations of Rayleigh scattering in terms of single-el ectron transition-amplitudes has led to significant progress in our underst anding of the scattering process. The importance of relativistic, higher mu ltipole, and bound-bound contributions in calculating anomalous scattering factor deviations from form factor amplitudes must be emphasized. Accurate interpolation of cross sections in the three-dimensional space of scatterin g angle, photon energy, and atomic number, utilizing the available publishe d S-matrix data, has permitted extensive tabulation of differential scatter ing cross sections. S-matrix results may be compared with experiments to as sess their validity; they may be compared with simpler but more approximate approaches. to identify the extent of the utility of such approaches and t o develop simpler prescription schemes which can give results comparable to the S-matrix results. In spite of their many successes, the present second order S-matrix methods also have limitations and shortcomings, observed in certain recent experiments. We describe the explanation of these experimen ts in terms of a composite theory which also incorporates non-local exchang e and correlation effects. We end with a discussion of other future issues. (C) 1999 Elsevier Science Ltd. All rights reserved.