A Test for Polarization of Electron Waves by Reflection

HE experiment described in this article was undertaken to determine whether or not a beam of electron waves is polarized by reflection from the surface of a nickel crystal. It is similar in certain respects to the experiment with double Norrenberg mirrors by which one demonstrates the polarization of light by reflection from glass, and in others to the experiment by which Barkla established that X-rays may be polarized. It resembles most closely, however, the variation of the Barkla experiment performed by Mark and Szilard in which the first of the radiators was a crystal and a Bragg reflection beam proceeded to the second radiator. A homogeneous beam of electrons is directed at 45 degrees incidence against a [111} -face of a nickel crystal, and the beam proceeding in the direction of regular reflection from this crystal is then reflected at the same angle of incidence from a second similar crystal. A double Faraday box is placed to receive electrons which have been regularly reflected from the second crystal, but only such electrons are allowed to enter the collector as have retained all or nearly all of their kinetic energy through the two reflections; those which have lost more than a small fraction of their kinetic energy are excluded by a retarding potential of suitable strength. The second crystal and the collector are joined rigidly together, and may be rotated about an axis which coincides with the axis of the beam proceeding from the first to the second crystal. It is possible, therel Phys.