Penetration and energy deposition of electrons in thick targets

Abstract

The transport and energy deposition of fast electrons in multilayer targets are investigated. For a highly peaked distribution function of electrons impinging on a target, it is necessary to use a high-order diffusion theory to adequately represent the distribution function. To a first approximation the energy loss is neglected in any given layer. The average energy loss per layer is then calculated using the Bethe stopping power and knowledge of the electron multiple scattering. Once the beam penetrates a distance of about one-fifth the transport mean free path, it becomes possible to use the Bethe age diffusion equations provided that the atomic number ≥ 13 and the electron energies are below 1 MeV. A combination of the diffusion and high-order diffusion theory is also used to compute the backscattered current and energy. Limitations and regions of validity of the above theories are also discussed.