Structure perfection of single-crystal quartz intended for experiments on finding the electrical dipole moment of neutrons by the crystal diffraction method

The perfection of quartz crystals of different origins intended for experiments on finding the electrical dipole moment of neutrons is studied. The study is carried out using the crystal diffraction method by passing a neutron through the crystal under near-Bragg conditions at a diffraction angle of about 90$^\circ$. It is shown that optical-grade quartz grown at the All-Russia Research Institute for Synthesis of Mineral Raw Materials (VNIISIMS, Aleksandrov, Vladimir oblast) offers the highest perfection and homogeneity. Of a total of 22 crystals, 15 best ones with a spread in the interplanar distance of $\Delta d/d_0\le$ 5 $\times$ 10$^{-6}$ were selected for experiments. The crystals measure 100 $\times$ 100 $\times$ 500 mm.