EFFECT OF COMPTON-SCATTERING ON THE DOUBLE-TO-SINGLE PHOTOIONIZATION RATIO IN HELIUM

The effect of Compton scattering on the ratio of double-to-single ioni zation from photon impact in helium has been measured for 2.1 less tha n or equal to h nu less than or equal to 5.5 keV using a time-of-fligh t ion spectrometer with a high relative collection efficiency for Comp ton ions. Single ionization from Compton scattering is found to contri bute measurably to a reduction in the ionization ratio for h nu greate r than or similar to 3.5 keV. Our measurements are compared with predi ctions based on recent calculations of the single and double ionizatio n 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 Suric et al. [ Phys. Rev. Lett. 73, 790 (1994)].