Cross-section ratio of double to single ionization of helium by Compton scattering of 40–100-keV x rays

We have measured the ratio of cross sections for double to single ionization of helium by Compton scattering, R-C = sigma(C)(++)/sigma(C)(+), at photon energies of 40, 80, and 100 keV using cold target recoil-ion momentum spectroscopy. Comparison with calculations involving highly correlated initial states and approximate final states with and without final-state correlations, represented by 3C and 2C wave functions respectively, shows that the influence of final-state correlations persists to very high photon energies. A comparison with recent charged-particle data is made. [S1050-2947(99)04701-0].