The scattering of high-energy photons by electrons. High-energy (662 keV) photons in a collimated beam from a radioactive
137 Cs source are scattered from electrons in a target which is itself a scintillation counter which detects the recoil electron. The scattered photons are detected in a second scintillation counter. The distribution in size of pulses from either the target or the scatter counter are recorded by a multichannel analyzer gated by pulses from a coincidence circuit activated by coincident pulses from the two detectors. In the first part of the experiment both scintillators are NaI crystals, and the energies of the scattered photons and the recoil electrons are measured as functions of the scattering angle; the results are compared with the theory of Compton scattering. In the second part the target is a plastic scintillator, and the relative intensities of scattered photons are recorded at several scattering angles. The results, normalized to a separate measurement of the total scattering cross section of the plastic scintillator, are used to derive the differential scattering cross section; the results are compared with the Thomson and the Klein-Nishina formulas for the scattering of photons by free electrons.
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