Vicinage effect on the yield of convoy electrons emitted from thin carbon foil induced by the penetration of 3.5-MeV/atom Cn+ 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 29.7μg/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.