Probabilities multiple electron-emission from thin (approximately 50 A) carbon foils after impact of neutral oxygen at energies between 30 and 200 Kev
Козочкина А.А., Леонас В.Б., Vitte M.
//Nuclear Instruments & Methods in Physics Research Section B-Beam Interections with Materials and Atoms, 1991. Vol. 62. Issue 1. С. 51-57.
The multiple secondary electron emission from a thin (approximately 50 angstrom) carbon foil has been measured for impacting primary oxygen atoms with energies of 30, 50, 100 and 200 keV. The absolute probabilities P(k), P(k'), P(kk') of the emission of k, k' = 0, 1 ... numbers of electrons in forward (k'), and/or backward (k) directions from the foil have been derived. It is observed that (i) the probabilities P(k), P(k') disagree with those expected from Poisson statistics, (ii) there is an asymmetry in the forward/backward emission, (iii) the probabilities P(k)(E) change in a different way with energy E than it is expected from the energy dependence of the stopping power dE/dx, (iv) in individual events there is no correlation between the numbers of electrons going in forward and/or backward directions.
From these observations and further statistical analysis it is concluded that the emission of multiple electrons is not the result of only one primary process (ionization by collision between the projectile and target atoms). Rather, larger numbers of emitted electrons are mainly produced in an additional process (cascade electron production), in which the internal secondary electrons produce further (tertiary) electrons.