Energy loss and straggling of protons in Tungsten

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

Limpopo, South Africa

Conferencia; 23rd International Conference of Atomic Collisions in Solids (ICACS) conference; 2008

We present a theoretical study on the energy loss by protons in solid Tungsten. First (stopping) and second (straggling) moments of the energy transferred from the ion to the target electrons, are calculated. The ab initio Shellwise Local Plasma Approximation (SLPA) is employed for the inner-shells, and the Mermin dielectric function for the valence electrons. The partial contribution of each sub-shell of target electrons is calculated separately, including the screening among the electrons of the same binding energy. Fully-relativistic wave functions and binding energies of W atom are calculated by solving numerically the Dirac equation using the HULLAC code. Results for stopping and straggling cross sections of protons in W, using these relativistic wave functions, are compared with the experimental data available. We analyze the role of the outer 4f-shell and the screening between electrons of near sub-shells (i.e. the 5p and 4f electrons). We also present new results of stopping cross sections for protons in Cu, to test the behavior of the SLPA with known Hartree-Fock wave functions. The theoretical curves are compared with the experimental data available. In the case of Cu, our results agree very well with the data and with the semi-empirical values. For W our calculations describe rather well the stopping measurements around the maximum and for very high energies, but overestimate the data in 10% for impact energies around 1MeV.