Charge state dependence of the stopping power of 1 MeV/A Ni-58 ions

The dependence of the energy loss of 60 MeV Ni-58 ions on the incident and analysed charge state was measured in thin carbon foils with a Q3D magnetic spectrograph. The surface contamination of the carbon foils was determined by elastic scattering of 12 MeV protons and included in the analysis of the energy loss data. Five incident charge states between q(in) = 8+ and q(in) = 18+ were selected. A reduction of the stopping power in the first few atomic layers is observed for low incident charge states and an enhancement for high ones with the transition occurring at q(in) approximate to 13.5. The results are discussed in terms of a reduction of the dynamic screening of the effective charge of the projectiles at the target surface.