A relationship between ionization by photons and by energetic charged particles interacting with matter is proposed and tested. The method is based on the recognition that both dipole and nondipole transitions are allowed for charged particles. The dipole component is shown to be related to photoabsorption, and the nondipole component to Compton scattering. As an example, we calculate the ratio of double to single ionization of helium by protons in terms of the corresponding ratios for photoabsorption and Compton scattering. At a proton energy of 400 MeV, this ratio is found to be 0.272%, with the dipole component contribution 0.211% and the nondipole component contributing the remaining 0.061%. The basic idea of our method may be readily extended to other many-electron processes, such as double excitation and excitation-ionization.

• Received 8 December 1994

DOI:https://doi.org/10.1103/PhysRevA.51.4687