Elastic scattering of 7.9-MeV photons from ¹⁸¹Ta

Differential cross sections for elastic scattering of 7.9-MeV photons from ¹⁸¹Ta have been measured at angles ranging from 25 to 140°. These results and previously measured differential cross sections from ²³⁸U and ²³²Th are compared with theoretical predictions taking into account Rayleigh scattering, nuclear Thomson scattering, nuclear resonance scattering, and Delbruck scattering. It is shown that at this energy the forward elastic scattering at angles ≤75° is due almost entirely to Delbruck scattering. The experimental results were found to deviate systematically from predicted values throughout most of the angular range. A striking agreement with theory was obtained only after excluding the contribution of the real part of the Delbruck scattering amplitude. [NUCLEAR REACTIONS Ta181(,), E=7.9 MeV; measured Delbruck scattering,σ(Θ), Θ=25-140.]