Ionization of Helium, Neon, and Nitrogen by Helium Atoms

The ionization cross sections for He and Ne atoms and ${\mathrm{N}}_{2}$ molecules on impact with He atoms have been measured over the laboratory energy range from 30 to 1000 eV. The incident atomic He beam was produced by the technique of ionization by electron impact, electrostatic acceleration, and neutralization by charge transfer. The measurements were carried out in a low-pressure parallel-plate ionization chamber. Particular attention was paid to the problem of secondary electrons. The ionization cross sections obtained for the He-He and He-Ne interactions were one to two orders of magnitude smaller than the ${\mathrm{N}}_{2}$-${\mathrm{N}}_{2}$, ${\mathrm{N}}_{2}$-${\mathrm{O}}_{2}$, and ${\mathrm{O}}_{2}$-${\mathrm{O}}_{2}$ cross sections studied earlier. The He-${\mathrm{N}}_{2}$ cross section was found to be of the same order of magnitude as the ${\mathrm{N}}_{2}$-${\mathrm{N}}_{2}$ cross section. Data were also obtained on ${\mathrm{He}}^{+}$-in-He charge transfer and secondary-electron emission from a gold surface by He ions and atoms.