Incoherent scattering of gamma rays byK-shell electrons

Differential cross sections for incoherent scattering by $K$-shell electrons have been measured, using coincidence techniques, for incident photons having energies of 662, 320, and 145 keV. Observations were made of the spectral distributions of scattered photons emerging at scattering angles ranging from 20° to approximately 140°. Target materials were iron, tin, holmium, and gold at 320 keV; tin and gold at 662 keV; and iron and tin at 145 keV. A typical spectrum generally displays a scattered quasi-Compton peak which is usually much narrower than would be expected from the bound-state electron motion. Rather than monotonically increasing with atomic number, the peak width typically reaches a broad maximum between $Z=50\mathrm{}$ and $Z=67\mathrm{}$ and then decreases with increasing atomic number. The peak, also typically, reaches a broad maximum width for scattering angles between 45° and 60°. No Compton defect is observed to within ±20 keV. Underlying the quasi-Compton peak is a continuum which diverges at the low end of the scattered-photon spectrum for the following cases: gold, holmium, and tin targets for 320-keV incident photons; gold and possibly tin targets for 662-keV incident photons. This infrared divergence (IRD) is expected on general grounds and has been predicted. The observed IRD continuum is very nearly isotropic.