STOPPING POWER FOR PROTONS IN ALUMINUM

The electronic stopping power of aluminum metal for protons has been calculated with explicit account taken of the different charge states of the photon inside the medium. The fraction of negative ions (H-) neutral atoms (H-0) and bare protons (H+) in the beam as a function of ion speed are derived from the capture and loss cross-sections. The total stopping power is then obtained by weighting the calculated partial stopping powers with the appropriate charge state fractions. The energy loss per unit path length due to electronic exchange processes is also evaluated. Our calculations show that the relative contribution to the stopping power from capture and loss processes is of the order of 15% for the case of protons moving in aluminum. Good agreement with experimental data is found.