Ionization by positive ions

Abstract

We describe a method of measuring the ionization cross-section of atoms by positive ions, in which electrons are collected from single collisions of an ion beam passing through a gas at low pressures. Secondary electrons formed by the collisions of ions with surfaces are suppressed. Measurements are given for twenty-three cases, over energy ranges of ~ 5 to ~ 40 keV (§ 1) and ~ 100 to ~ 3 keV (§2). The cross-sections do not appear to conform to the simple adiabatic theory, but the size of cross-section in the adiabatic region appears to depend upon the reduced mass of the system.