An expression for the charge-deposition distribution near the surface of a semi-infinite medium irradiated by electrons

On the basis of the characteristics of electron transport, a semiempirical model has been developed to describe the charge-deposition distribution due to knock-on electrons produced by electron-electron interactions near the surface of a semi-infinite medium. A criterion is provided for the thickness of the zone near the surface where the charge deposition is essentially due to knock-on electrons. A comparison between the charge-deposition distributions obtained by the Monte Carlo method and the present model is made in the above zone. The absorber materials considered are Be, C, Al and Cu, and the energies of incident electrons are from 1 to 10 MeV. The advantages and limitations of the present model in comparison with other analytic expressions are discussed