LAUSR

Abstract Rayleigh scattering differential cross sections for the 45.2 keV ( 66 Dy Kα 2 ), 46.0 keV ( 66 Dy Kα 1 ) and 52.1 keV ( 66 Dy Kβ 1,3 ) X-rays have been measured at 139° in 44 elements with 22 ≤ Z ≤ 90. The measurements were performed using a radiation source consisting of an annular 66 Dy foil excited by the 59.54 keV γ -ray photons from 241 Am radioactive source. Intensity of the incident photons along with other geometrical factors were determined by measuring the isotropically emitted K X-ray yields from targets and knowledge of the corresponding K X-ray fluorescence cross sections. The measured Rayleigh scattering cross sections are compared with those based on various form factor formalisms and the state-of-the-art S-matrix calculations to differentiate between their relative efficacies. The scattering cross sections based on the modified form factor (MF) formalism exhibit large deviations for the elements with electron binding energies in vicinity of the incident photon energy, and these deviations smooth out on inclusion of the anomalous scattering factors (ASFs) to the MF values. The cross sections based on the MF after including ASF's are found to be on an average higher by ~ 8% as compared to the measured ones. The S-matrix values exhibit in general good agreement with the measured cross sections for the elements with 22 ≤ Z ≤ 90.