COHERENT BREMSSTRAHLUNG AND CHANNELING RADIATION FROM 40 AND 150 GEV ELECTRONS AND POSITRONS TRAVERSING SI AND DIAMOND SINGLE-CRYSTALS NEAR PLANAR DIRECTIONS

Along planar directions in both Si and C single crystals the radiation yields from 150 GeV electrons are enhanced 40 times or more and the data present the first use of C crystals in the multi-hundred GeV region. For channeled electrons in Si the experimental results agree with calculations using the constant field approximation (CFA). Increasing incident angles reduce rapidly soft photon yields as expected from first order corrections to CFA. The first Born approximation only describes experimental results for large incident angles to planes.