Energy loss straggling of fast ions in solids

C. C. MONTANARI; J. E. MIRAGLIA; S. HEREDIA-AVALOS; R. GARCIA-MOLINA; I. ABRIL

Berlin

Congreso; 22th International Conference on Atomic Collisions in Solids (ICACS); 2006

ICACS Inernational Committee

We present theoretical calculations of the energy loss straggling of C, Al, Si and Cu targets for H, He and Li projectiles in the range of intermediate to high energies. These calculations have been done by employing the dielectric formalism and by considering the different equilibrium charge states of the swift ion inside the solid as a function of its energy. Two different models are used: the MELF-GOS (Mermin Energy Loss Functions combined with Generalized Oscillator Strengths) [1] and the SLPA (a shell-wise application of the Local Plasma Approximation) [2]. The results obtained by the two independent models are compared with the experimental straggling data of the latest twenty five years, which take into account the contribution of roughness and nonhomogeneity of the sample. We infer tree conclusions from the systematization made. First, the energy loss straggling tends at high energies to the Bohr value, and takes values below it at intermediate energies, the Livingston-Bethe shoulder does not appear in the present results. Second, the straggling normalized to Z2 is almost independent of the ion atomic number Z, therefore the results for H, He and Li projectiles in each target can be approximated by a universal band. Third, the contribution of each shell of target electrons saturates to a value proportional to the number of electrons in the shell.