Projectile dependence of ion-induced electron emission from thin carbon foils

The total secondary-electron yield from thin carbon foils traversed by heavy ions has been measured as a function of the projectile atomic number ${\mathit{Z}}_{\mathit{p}}$, the initial charge state, and the incident velocity. For nearly all projectiles in the velocity region studied the number of emitted electrons per incoming projectile γ and the stopping power S have, as expected, the same velocity dependence. However, for ions with ${\mathit{Z}}_{\mathit{p}}$>29 a slight increase of the ratio Λ=γ/S with the projectile energy is observed. A systematic study of the ratio Λ as a function of the projectile atomic number ${\mathit{Z}}_{\mathit{p}}$ indicates a ${\mathit{Z}}_{\mathit{p}}^{\mathrm{-}0.2}$ dependence of the parameter Λ. Possible explanations for this ${\mathit{Z}}_{\mathit{p}}^{\mathrm{-}0.2}$ dependence of the Λ parameter are given.