Impact-parameter dependence of proton-inducedK-shell ionization of carbon and aluminum

The impact-parameter dependences of the ionization probability of the carbon and aluminum $K$ shells by proton impact have been measured in a proton-x-ray coincidence experiment. Influences of the fluorescence yield and of the multiple scattering of the projectiles inside the target foils on the evaluation of the ionization probabilities have been investigated. The experimental results are compared with existing theories. Whereas the aluminum data can be explained by Coulomb ionization if adiabatic relaxation of the $1s$ state is taken into account, the experimental results for carbon exceed the theoretical values, especially at small impact parameters. Several possible reasons for this result are discussed.