Double-ionization processes in helium by photon and electron impact are analyzed, and it is shown that the inclusion of atomic correlation is very important. Detailed calculations are performed for the case of photo-ionization over the whole range of photon energies, and the asymptotic behavior of the cross section in the limit of large photon energies is discussed. Excellent agreement is found with recent experimental data. Conclusions are drawn concerning the related electron-impact problem at high incident electron energies. The leading term of the cross section is evaluated, and comparison is made with the presently available experiments.

• Received 13 July 1967

DOI:https://doi.org/10.1103/PhysRev.164.1