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Differential cross sections for elastic scattering of photons by C-12 and O-16 are measured at 58 and 75 MeV photon energies and 45 degrees to 150 degrees scattering angles using the tagged photon ...

Differential cross sections for Compton scattering by 4He have been measured at photon energies ranging from 83.7 to 93.8 MeV with a weighted average of 87 MeV using the bremsstrahlung beam of the MAX-LAB (Lund) nuclear-physics facility. The experimental differential cross sections show a pronounced increase at backward angles, strongly differing from predictions based on zero-angle dispersion relations and on the standard method used to calculate the differential cross section at nonzero angles. It is shown that the attempt to explain this effect in terms of quadrupole strength leads to unreasonable properties of the photoabsorption cross section. A parametrization in terms of a shift in the multipolarity ratio of the electromagnetic polarizabilities of the bound nucleon leads to Δβ = − Δα = 7 × 10−4 fm3.

Using recent experimental results on Compton scattering by 208Pb at energies below pion threshold we explore the effects of enhancement due to mesonic currents and isovector vibrations on the giant resonances of nuclei. Quantitative information is given for the enhancements of the electric polarizability, the diamagnetic susceptibility and the energy-weighted quadrupole sum rule. It is shown that the average of results available from different laboratories on the “nonretarded” enhancement constant KGDR in the A = 197–209 mass range favours an effective nucleon mass of m ∗ m = 3 4 . Some new results for the amplitude of Compton scattering by the giant resonances of nuclei are presented which allow a treatment of the retardation problem in a zero-order approximation.