Double Ionization of Helium by Fast Protons

Born approximation calculations are presented for the cross section of the double ionization of helium by 1-3-meV protons. The wave functions of helium are approximated by products of hydrogenlike, one-electron orbitals. Physically reasonable values of the screening parameters involved are used in the calculations. The results are compared with the two existing sets of experimental values for the production of ${\mathrm{He}}^{++}$ by protons. The calculated values are found to agree more closely with the second experiment than with the first. However, the calculated cross section decreases with increasing proton energy as $E^{-0.83\mathrm{}}$ which is considerably slower than the experimental values of $E^{-1.37\mathrm{}}$ and $E^{-1.16\mathrm{}}$.