Ionization Yields in Gases under Electron Irradiation

Abstract

The total number $N_{i}(T)$ of ionizations that an incident electron of kinetic energy T generates in a pure gas at low pressure obeys an integral equation known as the Fowler equation. Data show that its solution approximates $N_{i}(T)=(T-U)/W_{a}$ for T exceeding many multiples of the first ionization energy I, where U and $W_{a}$ are constants having the energy dimension. Attempts are made to derive formulas that express U and $W_{a}$ in terms of various cross sections for electron inelastic collisions with a gas molecule. The paper also describes the background of the problem and includes a critique of underlying assumptions that are often left unmentioned.