Charge Exchange Cross Sections of Hydrogen Particles in Gases at High Energies

Measurements are reported of the cross section for electron loss (σ₀₁) and electron capture (σ₁₀) for hydrogen atoms and ions traversing gases of hydrogen, helium, nitrogen, and argon. The kinetic energy of the particles was from 250 kev-1 Mev. Cross sections for electron loss were determined by measuring the attenuation of a neutral monatomic hydrogen beam in a gas cell in which a transverse electric field was present. The cross section for electron capture was measured by determining the fraction of the beam in each charge state after passing through a "thick" gas target. The fraction of the neutral component to the charge-one component is equal to the ratio of the cross sections for electron capture to electron loss. The velocity dependence of the cross section does not follow a strict power law. In hydrogen the cross section decreases approximately as v^-10, while for heavier target gases the velocity dependence is smaller, being v^-3.7 for argon at energies greater than 500 kev. The electron loss cross section has a 1v² dependence for gases of hydrogen and helium and a 1/v dependence for nitrogen and argon target gases.