Ultra-High Vacuum. II. Limiting Factors on the Attainment of Very Low Pressures

Abstract

Recently developed ultra‐high vacuum techniques, with which it is possible to achieve working pressures of 10⁻¹⁰ mm Hg or less, have made feasible the investigation of a number of physical processes occurring at very low pressures. The Bayard‐Alpert ionization gauge has been calibrated over its useful range and some of the important limitations on the production and measurement of ultra‐high vacuum have been determined. It has been shown that an ultimate limitation on the achievement of very low pressures in glass systems is caused by the diffusion of atmospheric helium through the walls of the system. A simplified omegatron has been developed for the measurement of the partial pressures of residual gases in a highly evacuated system.