ELASTIC-SCATTERING OF 22.1-KEV PHOTONS BY ELEMENTS IN THE ATOMIC REGION 2-LESS-THAN-OR-EQUAL-TO-Z-LESS-THAN-OR-EQUAL-TO-92

Differential cross sections for the elastic scattering of 22.1-keV pho tons by 30 elements in the atomic region 12 less than or equal to Z le ss 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 photo ns, 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 scat tering cross sections have been compared with those obtained in the in dependent-particle approximation through calculations of modified-rela tivistic form factors (MF's), a combination of MF's and angle-independ ent ''anomalous'' scattering factors (ASF's), and the relativistic sec ond-order S matrix. The MF values are found to be enormously larger th an 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 combin ation 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 d eviations increase up to 20% in case of elements with K-shell or L-1-s ubshell binding energy just below the incident photon energy, and furt her decrease to similar to 5% in case of elements with K-shell binding energy above the incident photon energy. The measured values for Al a nd Mg having electron binding energies far away from the incident phot on energy show good agreement with different calculations.