Consistency test of double ionization of helium by photons and charged particles

The authors have performed a consistency test of recent data for the ratios of cross sections of double to single ionization of helium by photons and by fast charged particles. It is based on a relationship that connects the dipole and nondipole components for cross sections by charged particle impact to photoionization and Compton scattering, respectively. The authors find the high energy ratio Rz for charged particles to be a sensitive probe of the photoionization data near threshold. Using recent experimental and theoretical data for photoionization, the asymptotic ratio Rz is found to range from 0.240% to 0.295%, as compared with direct experimental measurement of 0.26%