CHANNELING RADIATION OF ELECTRONS IN NATURAL DIAMOND CRYSTALS AND THEIR COHERENCE AND OCCUPATION LENGTHS

Measurements have been performed at the superconducting Darmstadt elec tron linear accelerator (SDALINAC) to investigate systematically chann eling radiation produced by bombarding natural diamond crystals with t hicknesses of 13, 20, 30, and 55 mu m with electrons at 5.2 and 9.0 Me V. Planar channeling from the (110) and (111) planes was studied for a variety of transitions with respect to their energy, intensity, and l inewidth. Axial channeling from the (110) axis could be detected as we ll. It was found that the intensity increases as a function of the cry stal thickness, and values up to 7.7 x 10(-2) photons/esr could be obt ained, which is the highest intensity at low electron energies achieve d so far. The intensity increases with electron energy as gamma(5/2). The 1/e occupation length deduced from the photon yield as a function of the crystal thickness was found to be l(occ) similar to 29 and 85 m u m for planar and for axial channeling, respectively. These values ar e by far the largest ever observed. Comparison with a quantum mechanic al theory of channeling radiation exhibits fairly good agreement for t he intensity and linewidth provided that contributions caused by elect ronic scattering and Bloch wave broadening, which actually are largest for diamond, are properly taken into account. it turns out that multi ple scattering dominates in the planar case and single scattering for the axial channeling. The coherence length could be deduced to be of t he order of 0.7 mu m, which is about a factor of 2 larger than observe d before in silicon.