Compton scattering of 279.2-keVγrays byK-shell electrons

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Abstract
Coincidence techniques have been employed in a detailed study of Compton scattering of 279.2-keV γ rays by K-shell electrons of tin and gold. Double-differential cross sections at four angles have been determined from about 30 keV to the kinematic limit. In the case of gold, clear evidence has been obtained for the infrared divergence effect predicted by Gavrila, and for Compton defects towards lower energies. The data obtained with tin do not show significant infrared divergence or Compton defects. The widths of the fully developed quasi-Compton peaks are about 85 and 55 keV in the case of gold and tin, respectively. A detailed investigation has been made of possible false coincidences arising from secondary processes. Energy-integrated single-differential cross sections have also been determined. Comparisons with other experimental data and with results of theoretical calculations have been presented. The experimental cross sections in the regime of low outgoing photon energies are much larger than nonrelativistic and relativistic theoretical predictions. The experimental data above about 100 keV are in much better agreement with the relativistic second-order S-matrix calculations of Whittingham, although at some angles deviations of about 30% are noticeable. The desirability of additional relativistic calculations and measurements with extremely thin targets has been pointed out.