HEAVY-ION-INDUCED ELECTRON-EMISSION FROM THIN CARBON FOILS

We have measured heavy-ion-induced (5 less-than-or-equal-to Z(p) less-than-or-equal-to 26; 0.3 < E < 1.8 MeV/u) secondary-electron emission (SEE) from thin carbon foils. For all projectiles in the velocity range studied, the SEE coefficient-gamma (number of emitted electrons per incoming projectile) and the stopping power S have the same velocity dependence. Similar to proton bombardment for heavy ions, we also observe a maximum of the yield of electron emission at energies very close to the stopping-power maximum. A systematic study of the ratio LAMBDA = gamma/S with the projectile atomic number Z(p) reveals a nonequilibrium regime for 1 < Z(p) < 6 ions (LAMBDA-decreasing with Z(p)) and an equilibrium regime for Z(p) greater-than-or-equal-to 6 ions (LAMBDA-independent of Z(p)). The obtained results are discussed in the framework of an extended Sternglass-type model, taking into account nonequilibrium projectile energy losses near the exit and entrance surfaces of the carbon foils.