Statistics of Transmission Secondary Emission from Thin Films of Alkali Halides

Abstract

The statistical distribution of the number of emitted secondary electrons per primary incident on transmission alkali-halide dynodes has been studied. For high primary energies (1 MeV), a model based on the theory of dielectric energy loss and the secondary electron-phonon interaction is proposed to account for statistical distributions. Measurements of distributions from 500-Å-thick films of CsI, KCl, and LiF have been carried out both at high energies and for primary energies near 9 keV corresponding to the maximum of secondary yield. It is shown that with some simplifying approximations, the model proposed can be used to calculate the distributions observed with high-energy primaries. Qualitatively, it is also possible to use the ideas proposed to understand the experimental results at low energy. Although in the literature the statement is often made that secondary emission distributions can be expected to be Poissonian, it is shown in this paper that there is very little firm basis for such a statement, and it is only through a knowledge of the detailed phenomena controlling secondary emission that a particular distribution can be predicted.