Calculation of energy loss straggling of C, Al, Si and Cu by H, He and Li ions

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

PHYSICAL REVIEW A - ATOMIC, MOLECULAR AND OPTICAL PHYSICS

American Physical Society

Año: 2006 vol. 75 p. 229031 - 2290311

1050-2947

We present theoretical calculations of the energy loss straggling of C, Al, Si and Cu targets for H, He and Li ions in the range of intermediate to high energies (10 keV/u - 10 MeV/u). 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) and the SLPA (a shell-wise application of the Local Plasma Approximation). The MELF-GOS describes the target outer-electron excitations through a fitting to experimental data in the optical limit, employing a linear combination of Mermin-type energy loss functions; the excitations of the inner-shell electrons are taken into account by means of generalized oscillator strengths. The SLPA employs a free-electron-gas model for the target valence electrons, and the local density approximation for each shell of target electrons separately, by using Hartree-Fock atomic wave functions. The results of the energy loss straggling obtained by the two independent models show a good agreement with the available experimental data. The calculated energy loss straggling tends at high energies to the Bohr value, and takes values below it at intermediate energies. The Bethe-Livingston shoulder (or overshooting) at intermediate energies does not appear in the present calculations. We find that the energy loss straggling normalized to Z_{P}² is almost independent of the ion atomic number Z_{P}, therefore the results for H, He and Li projectiles in each target can be approximated by a universal curve at high energies.