Planar channeling radiation from 54-110-MeV electrons in diamond and silicon

This paper reports the measurement of the differential photon yield per electron of planar channeling radiation and coherent bremsstrahlung emitted by 54-, 80-, and 110-MeV electrons incident on diamond and silicon crystals of various thicknesses (1-100 μm) and at several tilt angles relative to the incident beam. Information on the evolution of the electron transverse energy with the penetration depth, and thus on the relative population of the transverse energy states either bound or in the continuum, is obtained. All of the coherent-radiation processes are found to be well described by theories, except for the observed initial level populations, which differ markedly from predictions using the channeling wave functions. A discrepancy with theoretical models is also found for the incoherent radiation, but the influence of incoherent processes on level lifetimes is correctly predicted. The observed forbidden Δn=2 dipolar transitions may be due to the parity-breaking fluctuations in the potential.