The shellwise local plasma approximation, a collective model to describe bound electrons

C.C. MONTANARI, D.M. MITNIK AND J.E. MIRAGLIA

Itapema

Conferencia; 20th International Conference on Ion Beam Analysis; 2011

International Atomic Energy Agency (IAEA) and Ion Implantation Laboratory, UFRGS, Porto Alegre - Brazil.

The SLPA is a general method to calculate the contribution  of target bound electrons to the  different moments of the energy loss (ionization  cross sections, stopping, straggling) by  performing a space integration of the values in a localized region. It is inspired in the seminal  work by Lindhard and Scharff, and describes the response of the cloud of electrons of a certain  shell as that of an inhomogeneous density of electrons with an ionization gap [1].  This SLPA is valid within the perturbative limit, i.e.  linear response approximation within the  dielectric formalism. The only inputs are the densities of the sub-shells and the corresponding binding energies.  One of the advantages of the SLPA is that it deals with very heavy targets, like Au (79  electrons, 4f-subshell complete) with the same degree of complexity of much simpler ones, like  C or Al. On the other hand, the same formalism is employed to describe bound electrons of  solids or gas targets. We will present in this opportunity some results for the energy loss of ions in solids, like Zn, Cu,  Sb, Au or W [2-3], that combine the SLPA for bound electrons and a free electron gas  description for the valence ones. These results let us to analyze the ranges and limits of validity  of the model. We will also present calculated mean excitation energies and the comparison with Bethe high energy limit for the stopping power [1].  As  an additional test for this collective model we will also present  recent  fully theoretical  calculations (no parameters included) for ionization cross sections of K, L and M-shell of heavy  targets (50<Z<85) by different high energy ions. [1] C. C. Montanari, D. M. Mitnik, C. D. Archubi and J. E. Miraglia, Phys. Rev. A 80, 012901 (2009), and references therein. [2] C. C. Montanari, J. E. Miraglia, arXiv:0904.1386v1 (2009). [3] E. D. Cantero R. C. Fadanelli, C.C. Montanari, M. Behar, G.H. Lantschner, N.R. Arista and  J.E. Miraglia, to be published.