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

We 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 of cross sections by charged particle impact to photoionization and Compton scattering, respectively. We find the high energy ratio {ital R}{sub {ital Z}} for charged particles to be a sensitive probe of the photoionization data near threshold. Using recent experimental data for photoionization, the asymptotic ratio {ital R}{sub {ital Z}} is found to range from 0.240{percent} to 0.295{percent}, as compared with direct experimental measurement of 0.26{percent}. {copyright} {ital 1996 The American Physical Society.}