Elastic scattering of 22.1-keV photons by elements in the atomic region 12<=Z<=92

Differential cross sections for the elastic scattering of 22.1-keV photons by 30 elements in the atomic region 12 less than or equal to Z less than or equal to 92 have been measured at an angle of 117 degrees. The measurements were performed under vacuum using Si(Li) detector and Cd-109 radioisotope as photon source. The intensity of incident photons, detector efficiency, and other geometrical factors was determined by measuring the K x-ray yields from targets of various elements with 30 less than or equal to Z less than or equal to 52 excited by photons from Cd-109 and Am-241 radioactive sources and from the knowledge of K x-ray fluorescence cross sections. The present measured elastic scattering cross sections have been compared with those obtained in the independent-particle approximation through calculations of modified-relativistic form factors (MF's), a combination of MF's and angle-independent ''anomalous'' scattering factors (ASF's), and the relativistic second-order S matrix. The MF values are found to be enormously larger than the measured ones in case of elements with K-shell or L-1-subshell binding energy in the vicinity of 22.1-keV incident photon energy, and exhibit general agreement for other elements. The MF values in combination with ASF's and the S-matrix values are found to be on an average higher by 9% and 12%, respectively, than the measured values. These deviations increase up to 20% in case of elements with K-shell or L-1-subshell binding energy just below the incident photon energy, and further decrease to similar to 5% in case of elements with K-shell binding energy above the incident photon energy. The measured values for Al and Mg having electron binding energies far away from the incident photon energy show good agreement with different calculations.