Multiple ionization of noble gases by fully stripped ions

Absolute partial-ionization cross sections have been determined for inelastic interactions involving fully stripped atomic projectiles and noble-gas atoms. For helium bombarded with stripped H, He, Li, B, C, and O at reduced energies of 1.44 and 2.3 MeV/amu, the ratio of cross sections for double and single ionization R=σi2σi1 shows a strong dependence on the incident projectile charge. Furthermore, striking differences between results for equivelocity electrons and protons are observed, the ratio of double-to-single ionization by electron impact (∼2 MeV/amu) is almost a factor of 2 greater than that for proton impact, and the ratios for both particles converge only for reduced energies ∼10 MeV/amu. For neon targets, a similar strong charge-state dependence for incident, bare nuclei is observed, while the electron-proton discrepancy is considerably less. In contrast, the heavier noble gases all show a considerably weaker dependence of the cross-section ratio on the incident charge state.