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

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Abstract
The effect of Compton scattering on the ratio of double-to-single ionization from photon impact in helium has been measured for 2.1≤hν≤5.5 keV using a time-of-flight ion spectrometer with a high relative collection efficiency for Compton ions. Single ionization from Compton scattering is found to contribute measurably to a reduction in the ionization ratio for hν≳3.5 keV. Our measurements are compared with predictions based on recent calculations of the single and double ionization cross sections for photoabsorption and Compton scattering by Hino et al. [Phys. Rev. A 48, 1271 (1993), Phys. Rev. Lett. 72, 1620 (1994)], Andersson et al. [Phys. Rev. Lett. 71, 50 (1993)], and Surić et al. [Phys. Rev. Lett. 73, 790 (1994)].