The Effect of Small Angle Scattering on the Electron Absorption Coefficient

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Abstract
An indirect study of the scattering of electrons by gas molecules has been made by measuring electron absorption coefficients in an apparatus containing a Faraday cylinder of variable aperture. A straight path method was used in which electrons from an oxide-coated filament were given a desired velocity and made to traverse a 7.5 cm path to the collector. A retarding potential between the cylinder and its shield kept out all electrons which had suffered inelastic collisions as well as those which had been scattered outside of the collector opening. Measurements were made in argon, helium, hydrogen, and mercury vapor at accelerating potentials ranging from 11 to 196 volts. The radius of the cylinder aperture varied from one one-hundredth to one tenth of the path length. No consistent variation of the absorption coefficient with opening was found in any case. Theoretical calculations based on scattering laws obtained from inverse square or fifth power laws of force predicted relatively large variations. Calculations made assuming uniform scattering or the Sommerfeld law indicated small changes of the same order of magnitude as the deviations between individual values obtained in this experiment.

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