Effect of Compton scattering on the ratio of double to single photoionization of helium

A number of recent measurements and theoretical studies of the ratio of double to single ionization of Helium have concentrated on the asymptotic value of this ratio. However, none of the calculations have addressed the effect of Compton scattering on the ratio nor are the published data of sufficient statistical accuracy to delineate the effect. Based on the cross sections for photoionization and for Compton scattering it is expected that Compton scattering will contribute to the single ionization for photon energies greater than ∼2.5 keV and to both single and double ionization for energies greater than ∼4.5 keV. In fact, it will be the dominate contributor for photon energies greater than ∼6 keV. We will discuss these effects and present measurements of the double to single ionization ratio in the photon energy range where the energy transferred by the Compton scattering is sufficient to cause ionization