L-shell ionization cross sections of Ta, Pt, Th, and U by Si ion

C. MONTANARI, A. MENDEZ, D. MITNIK, M. OSWAL, S. KUMAR, U. SINGH, G. SINGH, K.P. SINGH, D. MEHTA, D. MITRA 5, T. NANDI 5.

Antibes

Conferencia; 24th International Conference on Ion Beam Analysis; 2019

Société Française du Vide

Accurate determination of the x-ray production cross sections is important because of theirwide use in atomic and molecular physics, and non-destructive elemental analysis ofmaterials. Reliable values of L-shell ionization cross sections are included in the extendedparticle induced x-ray emission technique (PIXE) [1]. In this opportunity we will present atheoretical experimental study of the L-shell ionization of relativistic targets. Themeasurements of x-ray production cross sections by (84-140 MeV) Si+q ions (q=8; 12),were held at the Inter-University Accelerator Centre of New Delhi. Multiple-holefluorescence and Coster-Kronig yields were used to obtain the Li ionization cross sections (i= 1-3) from the measured x-ray production cross sections Ll, Lα, and Lβ, Lη, and Lγ [2].The present experimental values are compared with full theoretical calculations by means ofthe shellwise local plasma approximation (SLPA) [2]. This model uses the quantumdielectric formalism to obtain the total ionization cross sections from an initial ground state.The wave functions and binding energies of the different targets were obtained by solvingthe fully-relativistic Dirac equation using the HULLAC code package [3]. Thesecalculations are based on first-order perturbation theory with a central field, including Breitinteraction and quantum electrodynamics corrections. The new experimental data and theSLPA results for the ionization cross sections of the Li subshells are also compared with theknown ECUSAR and ESPSSR [4], which are semiempirical approximations. The agrementbetween the SLPA values and the experimental is rather good, also with the ECUSAR.Interestingly, the cross sections are found to be almost independent of the charge state of theSi ions, and not the outgoing charge state of the ion. This is important because the meancharge state plays a decisive role in the multiple ionization during the ion-solid collisions.