The Absorption Coefficient for Slow Electrons in Gases

Abstract

Electrons from a heated filament were accelerated through a slit and deflected magnetically around a circular path into a Faraday cylinder connected to a galvanometer. From the plots of the logarithm of the ratio of the galvanometer current $G$ to the total electron current $M$ from the filament, as a function of the pressure, the absorption coefficients were determined for various accelerating voltages from 2 to 360. For a given voltage, the absorption coefficient was found to be independent of the current $M$ and also of the pressure (at about ${10}^{-2\mathrm{}}$ mm). The results of Mayer and Ramsauer were checked for argon and helium. In argon, the coefficient reaches a sharp maximum at about 12 volts, the value for 2 volts being only one-fifth of the maximum value. In helium there is a maximum at 4 volts. Methane gave a curve similar to these, with a maximum at about 7.5 volts, which is in agreement with the results of Akesson. The curves for nitrogen and carbon monoxide are nearly identical, both having a maximum at about 18 volts and a minimum at about 9 volts. The curve for hydrogen shows no maximum, the coefficient increasing steadily down to 2 volts.