Planar channelling in thick crystals

The passage of ultra relativistic electrons through a thick monocrystal has been considered, including multiple scattering. An asymptotic expression for the particle transverse energy distribution has been derived. It has been shown that a flux-peaking effect and an excess yield of δ-electrons occur at large penetration depth t and are determined by the balance between dechanneling and feeding. Due to the beam angular spread, these effects relax to zero as 1/''square root'' t. The absorption of δ-electrons leads to the saturation of their excess yield from a thick monocrystal in accordance with experimental measurements. (author)