Channeling radiation beyond the continuum model: The phonon "Lamb shift" and higher-order corrections.

Abstract

The quantum theory for channeling radiation from mega-electron-volt electrons is extended to include higher-order corrections from phonon scattering. The formalism developed to descrihe radiation line profiles may be applied to any radiating system exposed to extemal perturbations. For channeling radiation, it is shown that at electron energies above a few mega-electron-volts, the dominant correction to line energies is of third order in the strength of the interaction giving rise to phonon scattering. Detailed analytical expressions as well as simple estimates are derived for both the second- and third-order thermal corrections. Their magnitude, relative to line energies, is typically of the order of 10 -3 or less