Experiments on the Elastic Single Scattering of Electrons by Nuclei

Abstract

Experiments on the elastic single scattering of electrons by nuclei are described, the measurements extending over a range of voltages, angles, atomic numbers, and foil thicknesses. Observations were made at a number of voltages from 1.27 to 2.27 Mev and at angles from 20 degrees to 50 degrees on both sides of the incident electron beam. The scattering foils were aluminum, copper, silver, platinum, and gold, the atomic numbers thus varying from 13 to 79. When the foil thickness exceeded that for a "thin" target, a correction was made for multiple scattering. The use of an accurately focused homogeneous beam of electrons from an electrostatic generator made possible clear-cut control of the basic experimental variables. The experimental method was designed to minimize the effect of x-ray background, etc. The present results are in close agreement with the relativistic theory of electron scattering, as developed by Mott, over the entire range of the experimental variables except for the case of 2.27-Mev electrons on aluminum. Excepting only this case, the average of all the ratios of experimental result to theoretical prediction is 1.01 with a standard deviation of 0.06. This is in marked contrast with most of the previous work in this field where results have been widely divergent. The results of this paper, combined with spectroscopic data, extend the range of validity of the Coulomb law of attraction between electron and nucleus in close to the surface of the nucleus. The measurements of the scattering of 2.27-Mev electrons by aluminum will be repeated as soon as circumstances permit, as these results now indicate for the larger angles an interesting divergence from theory.