Delbrück contribution in the elastic scattering of1.115−MeVphotons

Abstract

Differential cross sections for the elastic scattering of 1.115-MeV photons from tungsten (Z=74) and lead (Z=82) have been measured at angles ranging from 30 deg. to 135 deg., using a high purity coaxial germanium detector. The experimental results are compared with S-matrix theoretical calculations of Rayleigh scattering cross sections, which also include contributions arising from the nuclear Thomson amplitudes and the Delbrueck amplitude in lowest order Born approximation. The present experimental data at 1.115 MeV indicates that Delbrueck amplitudes calculated with lowest-order Born approximation, when combined with S-matrix Rayleigh scattering amplitudes, are sufficient, as has previously been observed at 1.332 MeV for a number of high-Z elements, and at 1.121 MeV and 1.173 MeV for Z=92. This result for Z=74 and Z=82 at 1.115 MeV provides further confirmation that the Delbrueck amplitudes calculated with lowest-order Born approximation are sufficient for energies at and below 1.332 MeV, in contrast to the situation at 2.754 MeV where Coulomb corrections to the Delbrueck amplitudes are significant for high-Z elements.