Positron energy distributions from a hybrid positron source based on channeling radiation

A hybrid positron source which is based on the generation of channeling radiation by relativistic electrons channeled along different crystallographic planes and axes of a tungsten single crystal and subsequent conversion of radiation into e+e- -pairs in an amorphous tungsten target is described. The photon spectra of channeling radiation are calculated using the Doyle-Turner approximation for the continuum potentials and classical equations of motion for channeled particles to obtain their trajectories, velocities and accelerations. The spectral-angular distributions of channeling radiation are found applying classical electrodynamics. Finally, the conversion of radiation into e+e- -pairs and the energy distributions of positrons are simulated using the GEANT4 package.