The Scattering of Gamma-Rays by Nucleons

In order to explore the possibility that information concerning nucleon structure could be obtained from the scattering of photons of energy near meson production threshold, the cross section for the process has been calculated on the basis of the symmetrical scalar and pseudoscalar meson theories. The calculation was carried out in the non-relativistic, weak coupling approximation, neglecting nucleon recoil effects. No divergence difficulties were encountered. In the scalar theory, the proton total cross section is somewhat less than the Thompson cross section (${\sigma }_0$) as a consequence of intefrerence between the scattering by the nucleon and that by the meson cloud. In pseudoscalar theory the total cross section varies strongly with energy showing a resonance scattering effect with a peak value as high as $15 {\sigma }_0$. The angular distribution in the scalar theory is very similar to that given by the Klein-Nishina formula: $\left(\frac{1}{2}\right)(1+{cos}^2\theta )$. The pseudoscalar theory gives a quite asymmetric distribution, the form of asymmetry depending strongly on energy. The results may be taken as a strong indication that observation of the process could yield, in a sensitive way, information concerning the structure of the proton.