Influence of multi-electron charge-changing processes on the average charge states of heavy ions passing through a He-gas target

Average (equilibrium) charge states q¯ of heavy Acq+ (Z = 89), Noq+ (Z = 102) and Flq+ (Z = 114) ions passing through a He-gas target at energies 50-150 keV/u are calculated with account for single- and multi-electron loss and capture cross sections. The q¯ values are obtained by solving the balance equations for equilibrium charge-state fractions and using single-, double- and triple-electron loss cross sections and single- and double-electron capture cross sections. Calculations of all electron-loss and single-capture cross sections are performed using available computer codes, and double-electron capture cross sections are estimated using a new semi-empirical formula obtained in this work on the basis of available experimental data for He target atoms. The account for the multi-electron processes changes significantly (up to about 25%) the q¯ values compared with those calculated with only single-electron cross sections and leads to a better agreement with experimental data.