The Cross Section for Change of Charge and Ionization by High Velocity Metallic Ions in Hydrogen and Helium

Abstract

An experimental method was developed in which the primary ionization and change of charge effects of a beam of positive ions can be studied separately. The cross sections for change of charge and for ionization have been measured for ${\mathrm{Be}}^{+}$, ${\mathrm{B}}^{+}$, ${\mathrm{B}}^{++}$, ${\mathrm{C}}^{+}$, ${\mathrm{C}}^{++}$, ${\mathrm{Al}}^{+}$, ${\mathrm{Al}}^{++}$, ${\mathrm{K}}^{+}$, ${\mathrm{Fe}}^{+}$, ${\mathrm{Fe}}^{++}$, ${\mathrm{Fe}}^{+++}$, ${\mathrm{Cu}}^{+}$, ${\mathrm{Cu}}^{++}$, and ${\mathrm{Cu}}^{+++}$ ions moving through hydrogen and helium with velocities corresponding to accelerating potentials between 6000 and 24,000 volts. The determination of the cross section for change of charge was shown to be independent of the size and shape of the collectors used in the measurements, and the effects of scattered incident ions and of secondary electrons from various sources were shown to be negligible. A large energy difference was found between the ions formed in the gas by primary ionization and those formed by the change of charge process, the former having energies of the order of 10 ev and the latter having energies of about 0.1 ev or less. The cross-section values depend upon the type of ion and upon the accelerating voltage, and have magnitudes varying from less than 0.01 to 23\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ for hydrogen, and from less than 0.01 to 10\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ for helium.