The electron-positron pair production for a beam of very energetic photons (or ultra-relativistic charged particles) is predicted to be significantly enhanced when the beam is aligned along crystallographic rows of atoms. Channeling in crystals lowers the total energy of the created electron thus enabling the photon to decay in a one-step process. The new mechanism yields a rapidly increasing flux of electrons and positrons of comparable energies above a threshold near 30 GeV.

• Received 24 January 1983

DOI:https://doi.org/10.1103/PhysRevLett.50.950