Channeling radiation of electrons in natural diamond crystals and their coherence and occupation lengths

Measurements have been performed at the superconducting Darmstadt electron linear accelerator (S-DALINAC) to investigate systematically channeling radiation produced by bombarding natural diamond crystals with thicknesses of 13, 20, 30, and 55 μm with electrons at 5.2 and 9.0 MeV. Planar channeling from the (110) and (111) planes was studied for a variety of transitions with respect to their energy, intensity, and linewidth. Axial channeling from the $〈110〉$ axis could be detected as well. It was found that the intensity increases as a function of the crystal thickness, and values up to 7.7×${10}^{-2\mathrm{}}$ photons/esr could be obtained, which is the highest intensity at low electron energies achieved so far. The intensity increases with electron energy as ${\gamma }^{\frac{5}{2}}$. The $\frac{1}{e}$ occupation length deduced from the photon yield as a function of the crystal thickness was found to be $l_{\mathrm{occ}}\approx 29 \mathrm{and} 85$ μm for planar and for axial channeling, respectively. These values are by far the largest ever observed. Comparison with a quantum mechanical theory of channeling radiation exhibits fairly good agreement for the intensity and linewidth provided that contributions caused by electronic scattering and Bloch wave broadening, which actually are largest for diamond, are properly taken into account. It turns out that multiple scattering dominates in the planar case and single scattering for the axial channeling. The coherence length could be deduced to be of the order of 0.7 μm, which is about a factor of 2 larger than observed before in silicon.