Theory of pair creation in aligned single crystals

Abstract

The theory of pair creation by a photon in aligned single crystals, which is valid at any energies and incident angles, is developed. For small angles of incidence, the theory describes pair creation in the field of the axis (plane) of a single crystal. For this case, the corrections to the constant field approximation are found. For large enough angle of incidence, the general expressions are transformed into the standard theory of coherent pair creation. A modification of the coherent pair creation theory, which is valid in a wider interval of the incidence angles, is obtained.