Slowing down of hydrogen clusters in thin foils

We present experimental results for the energy loss in carbon of 10 to 120 keV/proton H n + clusters (up to n =25). Special attention is given to the ratio between the total energy loss of a H n + cluster and the total energy loss of n individual protons of the same velocity. At low cluster energies this ratio is less than unity, while it is larger than unity at high energies. Saturation effects with cluster size are observed at least for lower cluster energies. A theoretical model describing these effects is developed, and the theoretical results compare well with experimental data.