LARGE-ANGLE ELASTIC-SCATTERING OF 59.54-KEV PHOTONS BY ELEMENTS WITH 2-LESS-THAN-OR-EQUAL-TO-Z-LESS-THAN-OR-EQUAL-TO-92

Elastic-scattering cross sections for 59.54-keV photons have been meas ured at an-angle of 121 degrees for 42 elements in the atomic region 1 2 less than or equal to Z less than or equal to 92; The measurements w ere performed using a Am-241 radioisotope as the photon source and a S i (Li) detector. The measured cross sections have been compared with t hose based on the modified-relativistic form factors (MF's), a combina tion of the MF's and angle-independent ''anomalous'' scattering factor s (MF+ASF), and the relativistic second-order S-matrix calculations. T he MF cross sections are found to be enormously higher for the element s with K-shell binding energy (E-K) close to the incident photon energ y (E-inc) of 59.54 keV. The S matrix and MF+ASF cross sections, in gen eral, represent the trend of the measured data over the whole atomic r egion under investigation. These theoretical-cross sections are in goo d agreement with the measured data for the elements with 12 less than or equal to Z less than or equal to 26 and; thereafter, deviate with i ncreasing Z. The S matrix and MF+ASF values are: on the average, highe r by 17%, and 24%: respectively, for the elements with 39 less than or equal to Z less than or equal to 67; and by 10% and 19%, respectively , for the elements with 70 less than or equal to Z less than or equal to 92. In case of. Er-68, having a K-shell binding energy 2.1 keV lowe r than the incident photon energy, the MF+ASF value shows good agreeme nt with the measured one, and the S matrix value is lower by 12%.