Radiation from fast charged particles in crystals: Unified quantal treatment

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Abstract
We present a unified quantal treatment of the various types of radiation emitted by fast, charged, spin-(1/2) or spinless particles which propagate at small angles relative to a set of principal atomic planes or rows in a crystal. [Henceforth, direction(s) parallel or perpendicular to these rows (planes) will be referred to as longitudinal or transverse, respectively.] We analyze the dependence of the emission frequencies and rates on the energy and transverse momentum of the incident particle, distinguishing between two fundamental emission modes. One is the transverse mode (TM), which unifies all radiative transitions that are characterized only by the projected potential (i.e., the periodic transverse variation of the crystal potential), such as channeling, quasichanneling, and TM coherent bremsstrahlung transitions. The other one is the longitudinal mode (LM), which includes all transitions involving longitudinal momentum transfer to the lattice, with or without a simultaneous projected potential transition.