A Time-Of-Flight Electron Velocity Spectrometer for Low Energy Collision Measurements

摘要

A time-of-flight velocity selector is described that is designed for measurement of the total collision cross section of electrons in gases in the energy region below one volt, where beam-deflection methods are difficult and few data exist. The spectrometer essentially comprises a photoemitter, illuminated by a spark gap, separated by a shielded 0.45-meter drift path from a detector, consisting of an accelerating field and an electron multiplier, with electronic equipment for time and amplitude analysis and auxiliary apparatus for introduction of gases at known concentration. Design considerations are presented, followed by a description of the major components. Data illustrative of performance are given, together with initial transmission measurements in helium at electron energies down to 125 millivolts. Applications and extensions of the technique are discussed. (Author)