Electron-Electron Scattering at 6.1 Mev

The absolute differential cross section for the scattering of 6.1-Mev electrons by the electrons in a beryllium foil has been measured at 90 degrees and 109 degrees in the center-of-mass system. Electrons from a linear accelerator were first magnetically analyzed and then collimated to form the incident beam. Electron-electron scattering events were detected by end-window Geiger counters connected in coincidence. The counter with the defining aperture was connected in coincidence (1) with a counter at the conjugate scattering-angle, lying in the plane determined by the incident beam and the scattering direction to the defining counter; and (2), with another counter at the conjugate angle, but lying outside this plane, thus counting only accidental coincidences. The number of $e-e$ coincidences was then given by the difference between (1) and (2), with appreciable corrections arising from asymmetry in the background and from dead-time losses. These corrections required measurements of single and coincidence count rates with the scatterer in and out of the beam.