Ionization and Excitation of Atomic Li by Fast Ions

Abstract

Ionization and excitation of atomic lithium caused by the impact of nearly relativistic ions are considered, and the analogies with corresponding processes induced by incident photons are examined. Specifically, the nature of the interactions leading to single-electron ejection, and the mechanisms for producing doubly vacant K-shell states, are investigated. The bombarding particle for the studies discussed here is 95 MeV/u Ar¹⁸⁺ for which v/c = 0.42. First, single ionization (K-shell or L-shell) is found to consist of a part due to dipole transitions to the continuum (corresponding to photoionization) plus a part due to binary encounters between the fast projectile and a target electron (corresponding to Compton scattering). For the production of states with two K-shell vacancies, it is shown that the electron-electron interaction plays an important role in the formation of these so-called “hollow” states, in a manner similar to photon-induced processes. Atomic lithium provides a unique system in which to study ionization and excitation because of its tightly bound inner shell and weakly bound outer shell, and the fact that single- and double-K-shell vacancy production can be simultaneously investigated from a single Auger electron emission spectrum.