Vicinage effect on the yield of convoy electrons emitted from thin carbon foil induced by the penetration of 3.5-MeV/atom C n + ions

We investigated the convoy electron yields resulting from bombardments of amorphous carbon foils with 3.5-MeV/atom Cₙ⁺ ($n=1$--3) cluster ions. The target thickness ranged from 3.0 to 29.70.28em0exg/cm². A detailed analysis of the thickness dependence revealed that for bombardments with C₂⁺ and C₃⁺ ions, the convoy electron yield per atom, Yₙ/n, decreases with increasing target thickness and ultimately reaches an asymptotic value. The asymptotic value showed clear proportionality to the cluster size, n, indicating the presence of positive vicinity effects of Yₙ∝n². We found that the escape length of the convoy electrons for C₃⁺ and C₂⁺ is much longer than that of the C⁺ bombardment. The present result suggests that the enhancement of the escape length could be the origin of this vicinage effect on the convoy electron yield.