Electron-impact ionization of highly charged hydrogenic atomic ions

Electron-impact-ionization cross sections are calculated for hydrogenic ions with nuclear charge between 26 and 92, for incident electron energies up to 8 times the ionization energy, by a relativistic distorted-wave method. The results demonstrate the increasing importance of relativistic effects with {ital Z} and with incident electron energy, particularly for 1{ital s} ionization. The effects of including magnetic and retardation interactions as {ital Z} increases are also studied. Results are compared with scaled {ital K}-shell ionization measurements for {sup 47}Ag and {sup 79}Au.