STATISTICS OF ELECTRON-EMISSION INDUCED BY MEV H+ AND HE2+ IONS

In this work we describe an experimental setup for measuring the statistical distribution of the number of electrons which are emitted from a target surface at ion impact. Emission statistics is measured for MeV He-2+ and H+ projectiles impinging on Au and Cu targets. The total electron yield obtained from these measurements is compared to that obtained from current integration. The results agree within the estimated uncertainties of 3-5%. The distribution of the number of emitted electrons can be very well approximated by Polya distributions. For He-2+ impact this distribution is close to a Poisson distribution, whereas for H+ impact the measured distributions are completely different. It is shown that the deviations from Poisson statistics can be explained by the statistical distribution of the energy deposited by the projectile in a surface layer with a thickness which corresponds to the mean escape depth of ion induced electrons.