Absolute cross sections for multiple ionization of noble gases by swift proton impact

Absolute cross sections, sq+, for multiple ionization of He (q = 1), Ne (q = 1, 2, and 3), Ar (q = 1, 2, 3, and 4), Kr (q = 1, 2, 3, and 4), and Xe (q = 1, 2, 3, 4, and 5) atoms by protons in the 0.75-3.5 MeV impact energy range have been measured. The present results are in good agreement with the previously published data in the case of the single-and double-ionization cross sections, but some non-systematic discrepancies appear for higher charge states. A detailed comparison with electron impact cross sections in these gases is performed, and it shows that the cross sections for single ionization by high-velocity protons are substantially smaller than those corresponding to equi-velocity electrons for heavier targets.