Charge-state dependence of the exit energy of F ions traversing carbon foils

Abstract

A charge-state dependence has been observed for the exit energies of 0.87 MeV/u fluorine ions traversing carbon foils (1322̄5 μg/cm 2). Energy differences between ions exiting the foil in various charge states were measured by observing apparent shifts in the resonance energy of the 16.45 MeV resonance in the H 2( 19 F q+ , Heγ) 16O reaction and by direct observations with a surface barrier detector. It is found that emerging F 8+ions have an energy which is about 14 keV higher than that of F 9+ ions. The observed energy differences are largest for ions emerging with K-shell vacancies and small or zero for ions with a full K-shell and differing numbers of L-shell electrons. A semi-quantitative explanation of the results suggests that ions emerging with K-shell vacancies are produced in a relatively thin layer near the exit side of the foil and that the stopping power for these ions is charge-state-dependent.