Coherent radiation from 70 GeV and 150 GeV electrons and positrons traversing diamond and Si crystals near axial and planar directions

Channeling radiation and energy loss for 150 GeV electrons and positrons incident on a 0.5 mm thick 〈100〉 diamond and a 0.6 mm thick 〈110〉 Si crystal have been measured - near axial and planar directions. It is found that yields from well channeled electrons are enhanced by a factor of two, and those for positrons are reduced by a factor of five, as compared to yields outside the channeling region. The experimental critical angle for channeling agrees very well with the Lindhard angle ψ₁. For incidence along planes and close to axial directions, the overall picture of the radiation spectra for electrons and positrons is the same for the high-energy photons, where a strongly enhanced peak is found, as was first discovered in an earlier electron experiment. In diamond, the standard coherent bremsstrahlung has been measured close to the 110 planes but for 10 mrad and 50 mrad from the axis. These experimental results agree well with calculations using the Born approximation.