Energy loss of protons in W using fully relativistic calculations and mean excitation energies of W, Au, Pb, and Bi

C. C MONTANARI; D. M. MITNIK; C. D. ARCHUBI; J. E. MIRAGLIA

PHYSICAL REVIEW A - ATOMIC, MOLECULAR AND OPTICAL PHYSICS

American Physical Society

Año: 2009 vol. 80 p. 129011 - 129016

1050-2947

We present a theoretical study on the energy loss of protons in wolframiumby calculating target fully relativistic wave functions and bindingenergies. The extsc{hullac} code is employed to obtain numerical solutionsof the Dirac equation. We use the shellwise local plasma approximation(SLPA) to evaluate the different moments of the energy loss. The partialcontribution of each subshell of target electrons is calculated separately,including the screening among the electrons of the same binding energy. Wepay special attention to the role of the outer $4f$ shell and the screeningbetween electrons of near subshells (i.e., the $5p$ and $4f$ electrons).Results for stopping and straggling cross sections are compared with theexperimental data available. Our calculations describe rather well thestopping measurements around the maximum and for very high energies, butoverestimate the data for impact energies around 1MeV. We find that the SLPAresults tend clearly to Bethe limit, but show a systematic overestimation inthe energy region of 1-2MeV. This overestimation may indicate the presenceof other mechanisms included neither in the SLPA nor in Bethe formulations.We also present results for the stopping number of W, Au, Pb, and Bi whichfollow quite well the Lindhard scaling. A theoretical mean excitation energyI(W)=710 eV is obtained, in good agreement with the suggested value of 727 +/- 30 eV. Theoretical mean excitation energies for Au, Pb, and Biare also presented, which are in good agreement with the experimental ones.