Target inner-shells contributions to the stopping power and straggling for H and He ions in gold

Abstract

The electronic energy loss of swift H and He ions in gold is studied, paying special attention to the contribution to the projectile energy loss due to the ionization of the target inner-shells. We calculate the stopping power and the energy-loss straggling as a function of the projectile energy, taking into account the different charge states that the projectile can acquire inside the target and using the dielectric formalism. The electronic response of gold is described by the MELF-GOS model, where the excitation of valence and N-shell electrons is characterized by a linear combination of Mermin-type energy-loss functions, whereas the contribution to the projectile energy loss due to the target K-, L-, and M-shell ionization is included through hydrogenic generalized oscillator strengths. Stopping powers and straggling are, respectively, systematically above and below the data in our linear response formulation when H and He ions are below 0.1 MeV/u. Our calculations show that the total contribution of K-, L-, and M-shells to stopping power and straggling is less than 0.5% and 3.5% below 1 MeV/u, respectively. For stopping powers, the contribution of these inner-shells increases to 9% at 10 MeV/u and continues to rise to 20% at 100 MeV/u. For straggling, it increases to 23% at 10 MeV/u and rises to 35% at 100 MeV/u.