Inellastic collision calculations of heavy targets

D.M. MITNIK; C.C. MONTANARI; A.M.P. MENDEZ

Foz do Iguazu

Conferencia; The 9th International Symposium on BioPIXE; 2018

(Federal University of Rio Grande do Sul and e International Atomic Energy Agency (IAEA)

The description of heavy atoms requires the solution of the relativistic Dirac equation. To this end, we usedthe HULLAC code package [1], which allows one to obtain accurate relativistic one-electron orbitals andmulticonfiguration bound states and energies. The calculations are based on first-order perturbation theory with a central field, including the contribution from the Breit interaction and quantum electrodynamicscorrections. The detailed energy levels are computed using the RELAC code [2, 3], which uses the parametric potential model. This model consists in minimizing the first-order relativistic energy of a given setof configurations for a parametric analytical function for the screening charge distribution. Although thiscode was written for calculations of heavy ionized atoms, it can be successfully employed in other atomicsystems, such as the ones presented here.The binding energies obtained for Ta, Pt, Th and U (Z=73, 78, 90, 92) using the fully relativistic methodare shown with up-filled triangles in the Figure. The figure also includes experimental bound energies [4](hollow circles). The values computed for the inner orbitals agree with the experimental ones in about 2 %.The discrepancies found with the more external shells are accounted for the structure differences betweenthe atoms (computed) and the solids (experiments).The relativistic atomic structure calculated were used to compute inelastic collisional processes, such asenergy loss, straggling and L-shell ionization. In previous work, structure calculations were performed todescribe energy-loss and straggling of W, Au, Pb and Bi (Z=74, 79, 82, 83) [5, 6] for protons. L-shellionization calculations of these heavy atoms were also made in several theoretical approaches, showingvery good agreement with experimental results.