Ion-by-ion measurements of backward secondary electron emission of carbon foils under the impact of MeV H{sup +}, H{sup 0}, H{sup {minus}}, and H{sub 2}{sup +} projectiles

We have experimentally studied the backward electron emission from solid carbon bombarded by ${\mathrm{H}}^{+}$, ${\mathrm{H}}^{0}$, ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$, and ${\mathrm{H}}_{2}^{+}$ projectiles at MeV energies. We used a coincidence ion-by-ion technique that allows us to obtain not only the average electron yields but also the emission statistics. The comparison of energy dependences of electron emission due to ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^{0}$ projectiles helps to specify the role of the incident electron of ${\mathrm{H}}^{0}$. For ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{H}}_{2}^{+}$, the equality of electron yields above 500 keV/u supports the idea that backward emission is due to distant collisions.