Double and Single Ionization of Helium by 58-keV X Rays

Abstract

We have measured the ratio of cross sections for double to single ionization of helium by Compton scattering, ${R}_{C}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\ensuremath{\sigma}}_{C}^{++}/{\ensuremath{\sigma}}_{C}^{+}$, at a photon energy of 58 keV using cold target recoil ion momentum spectroscopy. We find a value ${R}_{C}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}({0.84}_{\ensuremath{-}0.11}^{+0.08})%$ that is in agreement with the asymptotic limits predicted by Andersson and Burgd\"orfer [Phys. Rev. A 50, R2810 (1994)] and Suri\ifmmode \acute{c}\else \'{c}\fi{} et al. [Phys. Rev. Lett. 73, 790 (1994)].