NUCLEAR PHOTON SCATTERING BELOW AND ABOVE THE GIANT-RESONANCES

Compton scattering on nuclei is studied from the general point of view in terms of matrix elements of microscopic nuclear operators in the low-energy region. The scattering amplitude is approximated by a consistent expansion up to second order in the photon energy where special care is taken about the low-energy Thomson limit. To extend the validity into the giant resonance region an explicit nuclear model is introduced to get analytic expressions for the scattering amplitude without any further approximation. The consistent treatment of the matrix elements leads to the occurrence of form-factor effects. An interpretation of scattering data on Pb-208 up to 50 MeV is given in terms of this model calculation. Additional excitation mechanisms are included in a phenomenological way.