Axial-channeling radiation from MeV electrons in various crystal targets

Abstract

Relativistic electrons and positrons under channeling conditions are steered by crystallographic planes (planar channeling) or axes (axial channeling). Their spontaneous transitions between the energy levels available for them in the transverse potential result in the emission of channeling radiation. The transverse axial potential for axially channeled electrons is obtained in the continuum approximation from a Nielsen-type interatomic potential. We introduce a parameter in the axial potential phenomenologically which is written heuristically to reflect the charge state and thermal vibrations of the target atoms. The channeling radiation energies from axially channeled electrons (of a few MeV energy) in diamond (C), silicon (Si) and germanium (Ge) are calculated. In diamond we show the dependence of radiation energies on axial channeling directions. Their dependence on thermal vibrations of target atoms and energy of the projectiles (electrons) is shown in silicon. The thermal vibrations reduce the channeling radiation energies. In germanium, the calculated radiation energy is compared with previous calculations. The agreement between the measured and our calculated values is quite good. Further calculations for Ni, Mo and W crystals have been performed to show that the assumed form of the parameter B is universal.