Energy loss of protons and helium ions passing through matter

Based on the dielectric-function method, together with the use of local-electron-density models (LEDM’s), the stopping powers of solid materials for the proton and helium-ion beams are investigated over a wide specific energy range from 1 keV/amu to 2.5×${10}^3$ keV/amu. The screening effect due to free electrons on ions with bound electrons is taken into account within the framework of the linear response. For a ${\mathrm{H}}^0$ atom in alkali metals, the screening effect increases significantly the stopping powers, while for a ${\mathrm{He}}^{+}$ ion it does not increase so much. The mean excitation energy is also calculated using the solid and the atomic LEDM’s. For a Ag target, not being a simple metal, we report how much the change in the number of free electrons affects the stopping cross section for a ${\mathrm{H}}^{+}$ ion. The charge-state distribution (CSD) suggested from the master curves of compiled stopping data is in agreement with the observed CSD. The calculated energy dependence of the effective charge of the helium-ion beams reproduces experimental data well.