Secondary electron emission from a thin carbon foil induced by H+, He2+ and Li3+ at fixed velocity of 1Â MeV/u

The statistical distributions of the number of forward- and backward-emitted secondary electrons (SE's) from a thin carbon foil have been measured simultaneously in coincidence with foil-transmitted H+, He2+ and Li3+ ions of 1 MeV/u in order to examine the forward-backward correlation of the SE emission (refer to as 'FB correlation' hereafter). With these projectiles, we have also measured the energy spectrum of SEs emitted from another carbon foil of similar thickness in the direction around 0° with respect to the incident beams. From the emission statistics data, it is found that both of the inclusive forward and backward SE yields divided by the square of the projectile atomic number (Zp) decrease with increasing Zp. This trend is qualitatively consistent with previous works by other authors. On the other hand, it has been certified from the energy spectra that the yields of binary electron scale well with Zp2. As for the FB correlation, the forward- or backward-emitted SE yield decreases gradually with increasing the number of SEs emitted in the opposite directions. This so-called 'negative FB correlation' appears to be pronounced for He2+ and Li3+ ions compared with that for H+ ions. Since low energy internal SEs do not contribute to the FB correlation, the observed Zp-dependent FB correlation seems to be consistent with the well Zp2-scaled production of high energy internal SEs and the decrease of the inclusive forward and backward SE yields with respect to this scaling.