INCOHERENT SCATTERING OF 662 KEV GAMMA RAYS ON THE K ELECTRONS OF LEAD

Large deviations from the Klein-Nishina differential cross-sections for inelastic scattering of gamma rays on electrons can be expected when the scattering electrons are strongly bound in the inner electron shells in heavy elements. Photons at 662 kev from Cs/sup 137/ were scattered on a thin lead target. Selection of inelastic scattering events on the K electrons in the target was attained by observing the scattered photons in coincidence with the K x-rays from lead. The cross sections per steradian were determined for the effect at three angles theta = 28 deg , 68 deg , and 132.5 deg , and were found to be 0.29, 0.87, and l.0 of the corresponding KleinNishina cross-sections, respectively. The coincidence gamma spectrum was displayed on a 100-channel pulseheight analyzer. Distributions of the scattered photons were found to be broader than those for the scattering on free electrons. No defect in the Compton shift was observed at harge angles, in contrast to early reports on scattering of low energy photons on light elements. In addition, the distribution of the photons scattered through 28 deg was found to be peaked at more » an energy about 48 kev smaller than that expected for free-ehectron scattering. An approximate treatment of the process is given in terms of the incoherent scattering function S, cahculated for the K electrons. (auth) « less