C. C. Montanari

A collective model for inner shell ionization of very heavy targets

We present a theoretical study of the ionization of inner shells, such as L and M shells of Au, Pb and Bi or K-shell of Sb. The ionization is described using a collective response model, the shellwise local plasma approximation (SLPA). This model deals with each sub-shell of target electrons as an inhomogeneous electron gas with an ionization threshold. No parameters are included, just the theoretical wave functions of the ground state and the binding energies. The validity range is that of the perturbative approximation, high energies and asymmetric projectile target relation. In the case of Sb, known Hartree–Fock wave functions and energies are used. Instead, for Au, Pb and Bi, they were obtained in fully relativistic way by solving numerically the Dirac equation. The SLPA describes well the experimental data for K-shell ionization of Sb by O and F positive ions. However, it underestimates the data for C or lighter ions. Good results are obtained for M-shell ionization of Au and Bi above 2 MeV/amu, and for L-shell ionization of Au and Pb above 10 MeV/amu. For L- and M-shells, the SLPA tends to underestimate the data for energies below the range of validity of the model but approaches the experimental data for higher energies.

The Dielectric Formalism for Inelastic Processes in High-Energy Ion–Matter Collisions

Abstract In this chapter we analyze the possibilities and ranges of validity of the dielectric formalism to deal with correlated bound electrons in matter by using the shellwise local plasma approximation. This model describes the response of the electrons of the same binding energy as a whole (collectively), screening the interaction with the impinging ion. It considers separately each sub-shell of target electrons, with the corresponding dielectric response. The density of electrons and the energy gap are included explicitly by employing the Levine and Louie dielectric function. The goal of this chapter is to summarize and review the capability of this model to deal with fundamental magnitudes of the atomic collisions expressed as different moments of the energy loss: ionization cross sections (single or multiple, differential, and total), stopping power (and mean excitation energy), and energy loss straggling. This review covers a wide range of the collisions of ions with gases and solids, paying special attention to multi-electronic targets. The advantages and disadvantages of the model in comparison with independent electron ones, ranges of validity and future prospect will be considered.

Effectiveness of projectile screening in single and multiple ionization of Ne by B2

Pure multiple ionization cross sections of Ne by B{sup 2+} projectiles have been measured in the energy range of 0.75 to 4.0 MeV and calculated using the continuum distorted wave-eikonal initial state approximation. The experiment and calculations show that the ionization cross sections by B{sup 2+}, principally for the production of highly charged recoils, is strongly enhanced when compared to the bare projectile with the same charge state, He{sup 2+}, at the same velocities.