Seção de choque parcial e total absoluta nas colisões de Li+ e Li2+ em Argônio, na faixa de energia de 0,2 a 3,5 MeV

Abstract

In order to understand the behavior of channels of electron loss, electron capture and direct ionization of the target (for a fixed one) it is necessary to understand how these channels are affected by the energy range of the projectile, by the charge state of it and if they are connected somehow. In the energy range studied in this work, the electron loss of the projectile may occur basically due to ways, namely the screening, antiscreening and the second-order process (“Loss Ionization – LI”). At low energies, the capture channel is dominant to the loss channel, and combination of low energy and charge state of the projectile may favor the coupling of these channels (loss - capture) in the same collision event, keeping fixed the charge state of the projectile before and after the collision. Furthermore, for many electrons target, the coupling between the capture and ionization channel must also be considered. To study how the channels of electron loss, electron capture and ionization are connected and competing during the collision, two types of measurements to Argon target were made: first, the measurement of the absolute total cross section for the loss and electron capture of Li+ and Li2+ in the energy range from 0.2 to 3.5 MeV. Second, the measure of the absolute partial cross sections for capture and loss channels (for the Li2+ projectile, leading to target multiple ionization) and the direct ionization of the target from 0.75 to 3.5 MeV. Experimental data for electron loss are compared with theoretical calculations based on the Plane Wave Born Approximation (PWBA) and the Free Collision Model (FCM). The theory-experiment comparison (PWBA-antiscreening + MCL-screening) for total electron loss channel (single + double loss) for the Li+ projectile shows a good agreement. In relation to the Li2+ projectile, on the same channel, it is observed a theory-experiment discrepancy, which can be attributed to the coupling between loss and capture channel in a single collision event (transfer-loss) and the second-order process (LI).