Electroproduction of electron-positron pair in oriented crystal at high   energy
  The process of electroproduction of the electron-positron pair by high energy electron in an oriented single crystal is investigated. Two contributions are considered: the direct (one-step) process via the virtual intermediate photon and the cascade(two-step) process when the electron emits the real photon moving in the field of axis and afterwards the photon converts into the pair. The spectrum of created positron(electron) is found. It is shown that the probability of the process is strongly enhanced comparing with the corresponding amorphous medium. 
V. N. Baier, V. M. Katkov