Study of a positron source generated by photons from ultrarelativistic channeled particles

Radiation by channeled electrons in germanium and silicon crystals along the <110> axis is studied as a very promising photon source of small angular divergence for positron generation in amorphous targets. Radiation rates for different crystal lengths-from some tenths of a millimeter to 10 mm-and two electron incident energies, 5 and 20 GeV, are considered, and a comparison between the two crystals is presented. The thermal behavior of the crystal under incidence of bunches of 10¹⁰ electrons is also examined. The corresponding positron yields for amorphous tungsten converters of 0.5 and 1 X₀ thickness are calculated for a germanium photon generator. Assuming a large acceptance optical matching system as the adiabatic device of the SLC (Stanford Linear Collider), accepted positrons are evaluated and positron yields larger than 1 e⁺/e^- are obtained