Total inelastic cross sections for slow electrons in xenon†

Abstract

An electron beam of low energy enters a cubic wire gauze chamber in Xe at a pressure of about 10−2 torr. The scattered electrons escaping from the chamber are received by a collector kept at a retarding potential of frac13; of the accelerating voltage. When inelastic collisions duo to excitation sot in, the collector current decreases. In order to derive from this change the absolute cross section, the average number of electron collisions in the chamber must be known; this was determined in two ways. With this result and the observed variation of the collector current with the accelerating voltage the total excitation cross section is found between the lowest excitation potential of 8-2 v and the ionization potential of 12-1 v; multiple scattering, energy spread and closeness of energy levels of Xe prevent the appearance of a fine structure. For energies up to 15 v approximate cross-section values are obtained after allowing for the positive ion current and including the known ionization cross sections. Further analysis of the results suggests that the transparency of the gauze is smaller than its geometric value, that it varies with the energy of the electrons and positive ions and that the ion concentration in the chamber is relatively large. The electron emission from the collector by Xe ions and metastable atoms seems to be insignificant.