Secondary electrons induced by fast ions under channeling conditions. II. Screening of fast heavy ions in solids

Abstract
Ion-beam shadowing effects have been observed for secondary electrons induced by various ions in the energy range of 1.8–3.8 MeV/amu, under various channeling conditions in Si and GaAs crystals. From a comparison of the energy spectra of electrons induced by ions of equal velocity, we have found reduced shadowing effects for heavy ions (Si, S, and Cl) as compared with light (H, He, C, and O) ions. It is concluded that the reduction results from the screening of the heavy ion’s nuclear charge by bound electrons. By analyzing the reduced shadowing effect, the effective nuclear charges for the heavy ions within the target crystals have been determined.