CHARGE-STATE DEPENDENCE OF THE STOPPING POWER OF 1 MEV/A NI-58-IONS IN THIN CARBON FOILS

Energy loss and energy straggling of 60 MeV Ni-58 ions in ultrathin carbon foils (0.8 to 30 mu g/cm(2)) have been measured with a Q3D magnetic spectrograph in dependence on the incident and analysed charge state of the ions. The stopping power in the first few atomic layers deviates significantly from the value in larger depths and can be scaled with the square of the incident charge state q. For larger depths the stopping power coincides with the tabulated value for all measured charge states. From this difference in the stopping power an average charge state ($) over bar q=15.5 for the Ni-ions inside the bulk can be estimated in a first approximation. With the average charge state behind carbon foils being ($) over bar q=17.6 the ion has to lose two electrons on average when leaving the target, e.g. by Auger processes. The energy straggling of the Ni-ions can be approximated by the known formula of Bohr. Nevertheless the systematics of the dependence on the incident and analysed charge state indicates that charge changing events contribute a significant amount to the energy straggling.