Calculation of Double Differential Cross Section for Fast Ion and Electron Impact Ionization of Atoms

The theory of the energy and angular distribution of electrons ejected in electron-atom and ion-atom collisions, within the framework of Born approximation, is discussed. Particular attention is paid to the case where the incident ion carries along its own electrons. Examples are given for e, H+, and He+ collisions with He. It is shown that for fast collisions, excellent agreement with experiment is obtained for electron impact and fairly good agreement for proton and He+ impact when both projectile and target ionization are taken into account.