Large-angle elastic scattering of 59.54-keV photons by elements with 12<~Z<~92

Elastic-scattering cross sections for 59.54-keV photons have been measured at an angle of 121° for 42 elements in the atomic region 12<~Z<~92. The measurements were performed using a ²⁴¹Am radioisotope as the photon source and a Si (Li) detector. The measured cross sections have been compared with those based on the modified-relativistic form factors (MF’s), a combination of the MF’s and angle-independent “anomalous” scattering factors (MF+ASF), and the relativistic second-order S-matrix calculations. The MF cross sections are found to be enormously higher for the elements with K-shell binding energy (E_K) close to the incident photon energy (E_inc) of 59.54 keV. The S matrix and MF+ASF cross sections, in general, represent the trend of the measured data over the whole atomic region under investigation. These theoretical cross sections are in good agreement with the measured data for the elements with 12<~Z<~26 and, thereafter, deviate with increasing Z. The S matrix and MF+ASF values are, on the average, higher by 17%, and 24%, respectively, for the elements with 39<~Z<~67; and by 10% and 19%, respectively, for the elements with 70<~Z<~92. In case of ₆₈Er, having a K-shell binding energy 2.1 keV lower than the incident photon energy, the MF+ASF value shows good agreement with the measured one, and the S matrix value is lower by 12%.