Measurements of Rayleigh scattering and relativistic calculations of incoherent scattering functions

Recent measurements of Rayleigh scattering employing neutron capture gamma -rays are presented. Experimental conditions are achieved such that the Ray leigh contribution is dominant and much larger than the other competing coh erent processes. A detailed comparison with the modified relativistic form factor (MRFF) approximation is made and it is concluded that the latter ove restimates the cross-section by 3-4%. New calculations of S, the incoherent scattering function, are presented in the relativistic treatment of Ribber fors and Berggren, using multiconfiguration Dirac-Fock relativistic wavefun ctions. 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 theta = 60 degrees 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 Angstrom (-1). In the region below 0.1 Angstrom (-1) the accuracy worse ns with decreasing momentum transfer, reaching 6% at 0.01 A(-1) and 10% at 0.005 Angstrom (-1). The same multiconfiguration wave functions were used t o evaluate new MRFFs. The new elastic scattering cross sections differ by 3 -6% compared with calculations based on single configuration wave functions . (C) 2001 Elsevier Science Ltd. All rights reserved.