Charge dependence of electron emission in swift heavy-ion collisions with carbon

Abstract

International audienceWe report on the charge dependence of electron yields from sputter-cleaned amorphous carbon targets bombarded with an isotachic set of swift ions. The experiments were performed in a UHV setup at the heavy-ion accelerator GANIL in Caen. The ion velocity was 19 a.u. (corresponding to a kinetic energy of 9.2 MeV/nucleon) and the projectile charge QP was varied from 6 to 39. As observed for ion-atom collisions, the electron yield exhibits a reduction with respect to a Q2P law. We show that this projectile charge dependence is consistent with a strong saturation of low-energy primary electron ejection. This effect is related to the primary projectile-target interaction itself and not to high-charge effects affecting the electron transport before escape from the target

Bombarding insulating foils with highly energetic ions

“…With heavy ions, such charging phenomena should become even more important, since electron emission yields are much higher than in the case of electron or proton impact. For a carbon foil, with protons as projectiles, less than 10 electrons per incoming projectile are emitted even around the maximum of the electronic stopping power, the yield dropping below one electron per projectile for 10 MeV protons [5]. In contrast, for a heavy Kr ion at 64 MeV u −1 , it can be estimated from known scaling relations [6,7] that about 130 electrons are emitted per incoming projectile: about 100 in the forward direction (beam exit side) and about 30 in the backward direction (beam entrance side) with a carbon foil of ≈130 μg cm −2 thickness.…”