Measurements of Rayleigh scattering and relativistic calculations of incoherent scattering functions

Abstract

Recent measurements of Rayleigh scattering employing neutron capture γ-rays are presented. Experimental conditions are achieved such that the Rayleigh contribution is dominant and much larger than the other competing coherent processes. A detailed comparison with the modified relativistic form factor (MRFF) approximation is made and it is concluded that the latter overestimates the cross-section by 3–4%. New calculations of S, the incoherent scattering function, are presented in the relativistic treatment of Ribberfors and Berggren, using multiconfiguration Dirac–Fock relativistic wavefunctions. Tables of S, for Z=1–110, are shown on a momentum transfer mesh identical to previous non-relativistic calculations. S has been calculated at a representative angle θ=60° and energies compatible with the presentation mesh. For other scattering angles, the values presented in the tables are accurate to within 1–2% for momentum transfers larger than 0.1 Å −1. In the region below 0.1 Å −1 the accuracy worsens with decreasing momentum transfer, reaching 6% at 0.01 Å −1 and 10% at 0.005 Å −1. The same multiconfiguration wave functions were used to evaluate new MRFFs. The new elastic scattering cross sections differ by 3–6% compared with calculations based on single configuration wave functions.