Angular dependence of specular resonant nuclear scattering of x rays

Specular scattering of x rays by electrons in a material becomes large at grazing angles below the critical angle for external reflection. In contrast, we observe specular scattering by resonant nuclei to peak at the critical angle and decrease at smaller angles. This is the result of the influence of the electronic scattering on the nuclear response of the system and is explained using an optical model. A distorted-wave Born approximation shows the specular nuclear signal should be large at angles where the electronic reflectivity varies rapidly with angle.