The Nuclear Scattering of 1-Mev Electrons and Positrons

The scattering of 1-Mev electrons and positrons by thin foils has been investigated from two points of view: (1) to compare the cross section for elastic nuclear scattering of positrons with that of electrons, and (2) to look for evidence of inelastically scattered electrons which have suffered large energy losses. The first experiment is of interest because theory predicts a large difference between electron and positron scattering as a result of spin-orbit coupling, and thus involves the magnetic moment of the electron. The second experiment is of importance because there have been many conflicting reports on the existence of inelastic scattering whereas theoretically one expects almost no inelastic scattering.Electrons and positrons from artificially radioactive sources were energy selected by a solenoidal spectrometer before being scattered by various foils. After being scattered, the particles entered a second, analyzer, magnetic field and were then detected by a Geiger counter. To study inelastic scattering of electrons the analyzer field was varied. To study the e^-e⁺ scattering ratio, various scatterers could be employed without changing the equipment in any way except to replace the electron source by a positron source. Thus the e^-e⁺ scattering ratio could be measured with greater accuracy than the scattering of either particle separately.The observed e^-e⁺ scattering ratio 2-3 is consistent with a rather rough theory which does not take into account screening. No inelastic scattering was found in foils of copper, aluminum, or platinum.