Coulomb Corrections to Delbrück Scattering

Abstract

Observation of Delbrück scattering is most feasible on heavy elements and in the 1-3 Mev region, where the Born approximation is expected to be very poor. The Coulomb corrections to the known forward scattering amplitude in Born approximation can be computed with the aid of the dispersion relations, making use of theoretical and experimental knowledge of the total cross section for pair production. Explicit calculations are carried out for a lead target. The results show that the corrections are effectively much smaller than anticipated. In the energy region of interest the corrections to the dispersive amplitude are only a few percent. The corrections to the absorptive amplitude are largest (a factor of two near 1.33 Mev) where this amplitude is negligible compared to the dispersive scattering amplitude.