Ionization by protons in the energy range 100 to 450 keV

Abstract

Ionization by protons in the energy range 100 to 450 keV has been investigated by means of the well-known parallel-plate condenser method. A uniform axial magnetic field enables slow ion collection to be carried out over a precisely determined path length at pressures low enough to ensure single collision conditions. The total cross-section for slow ion production cr+, and the total ionization cross-section have been determined for protons in hydrogen, helium , neon, argon and krypton. It is found that charge transfer is very small above about 200 keV so that cr+ ~ cr_e. The ionization cross-section for all cases falls off as E^-1 log E where E is the energy of relative motion. At the high-energy limit of the present measurements, the proton ionization cross-sections agree closely with electron ionization cross-sections for the same relative velocity of impact. The results are therefore in agreement with the general predictions of the Born approximation.