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Multiple Coulomb scattering in a crystal is anisotropic due to the presence of the coherent part in the Coulomb scattering cross section. This part depends on the crystal alignment and can be either increased or suppressed by the choice of the crystal alignment. As the result, the r.m.s. multiple scattering angle depends on the crystal orientation.
For the investigation of this process the experiment on Coulomb scattering of 855 MeV electrons was conducted at the Mainzer Mikrotron MAMI. Crystalline and amorphous silicon membranes both with a thickness of ~34 µm were used as targets. Multiple scattering angle was measured for the alignment of complete coherent scattering suppression, predicted by our model, as well as in a wide angular range. The experimental results were critically compared with our simulations and theoretical predictions.
We report the observation of the reduction of multiple Coulomb scattering in a crystal in comparison with the amorphous target. We demonstrate the maximal 7 % reduction of the r.m.s. multiple scattering angle at certain crystal alignment with the [100] crystal axes and partial reduction in a wide range of angles of alignment up to 15 degrees. Moreover, we observe the opposite effect, i.e. the increase of multiple Coulomb scattering at the orientation nearly parallel to the skew crystal planes.