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A test setup for measuring the neutron electric charge using spin interferometry and the effect of the double-crystal focusing of neutrons upon Laue diffraction is described. It is shown that a considerable increase in the distance between the crystals (up to 1 m) is needed to improve the accuracy of neutron-charge measurements. This is a difficult task because the setup becomes sensitive to slight external influences (temperature, vibration, etc.). To determine the degree of these influences, temperature tests with combined (active and passive) thermal protection were carried out. It is shown that under conditions of the reactor hall with temperature fluctuations of several degrees, the experimental setup provides a temperature stability of the crystals no worse than 0.01 K and stability of the temperature differences for the crystals and between them at a level of ~0.005 K. Measurements of the vibration level in the area of the PF1b cold neutron beam at the ILL reactor (Grenoble, France) allow estimation of the rate of displacement of crystals relative to each other at a level of ~10–3 cm/s. As follows from the data obtained, the angular resolution of the setup, without taking into account the influence of the imperfection of real crystals, can be at the level of 10–3 of the Bragg-reflection width, which is ~0.001 arc-second.

The spatial splitting of an unpolarized neutron beam into two spin components in an inhomogeneous magnetic field (an analog of the Stern-Gerlach experiment) with small gradients has been measured at the Laue diffraction in a crystal and Bragg angles θB = (78–82)° close to a right one. The spatial splitting of the beam at a path length of 21.8 cm has reached (4.1 ± 0.1) cm (at a maximum gradient of 1.5 G/cm and a diffraction angle of 82°). In the absence of the crystal, the splitting would be ∼ 3.8 × 10−7 cm at the same distance and gradient. The experimental enhancement coefficient is ∼ 105 tan2 θB, which is consistent with the theory.

The effect of neutron spin rotation at Laue diffraction in a weakly deformed neutron-transparent noncentrosymmetric crystal has been described theoretically and studied experimentally. The effect is due to the bending of a Kato trajectory of the neutron in the deformed crystal. At a certain type of deformation, one of two neutron waves excited at Laue diffraction, which propagate in opposite crystal fields in the crystal with no center of symmetry, leaves the crystal. As a result, the spin of the remaining neutron wave is rotated by a certain angle with respect to initial direction due to the interaction of the magnetic moment of a moving neutron with the crystalline electric field. This effect is absent in an undeformed perfect crystal, where only the depolarization of a beam occurs because both waves in opposite electric fields have the same amplitude. A method has been developed for controlled deforming the perfect single crystal by creating a temperature gradient in it. Thereby, a new possibility of measuring electric fields acting on a neutron in noncentrosymmetric crystals, as well as a method of controlling these fields in experiments on studying the fundamental properties of the neutron, has been implemented.

A prototype system design for ultra-high-precision neutron spectrometry using diffraction in perfect crystals is described. Results of experimental verification of the temperature stability inside the setup are presented. Results of vibration spectrum measurements in working zone of the PF1b beam of ILL reactor (Grenoble, France), where the prototype setup will be arranged for experimental testing, are considered.

A new mechanism of neutron acceleration in the accelerated perfect crystal is proposed and studied experimentally. The effect arises due to the resonance energy dependence of the neutron refraction index in vicinity of the Bragg's energy. During the neutron time-of-flight through the accelerated crystal the relative neutron-crystal velocity will be changing (with the deviation from the exact Bragg condition) and so the refraction index and the velocity of outgoing neutron will change as well.

The effect of neutron spin rotation at Laue diffraction in a noncentrosymmetric weakly deformed neutron-transparent crystal has been studied experimentally. The effect appears because of two phenomena: (i) the interaction of the magnetic moment of a moving neutron with the crystalline electric field and (ii) bending of trajectories of the neutron in a deformed crystal; as a result, the amplitudes of two waves excited at Laue diffraction, which propagate in the crystal in opposite electric fields, at the output of the crystal are not equal.

Review of the new crystal-diffraction methods to study fundamental neutron properties and interactions is presented. Features of neutron optics in the crystal without a center of symmetry is discussed as well as the first experimental results and perspectives to improve the sensitivity of experiments on a search for the neutron electric dipole moment (EDM) and CP-violating short-range pseudomagnetic nucleon-nucleon interaction. Also, the possibility to develop ultra-precise neutron spectroscopy using Laue diffraction in the perfect crystal is discussed, which can be used for a broad range of experiments: search for the neutron electric charge; test of the equivalence principle; precise measurements of neutron scattering amplitudes; crystal quality testing.

The effect of two-crystal focusing of neutrons at Laue diffraction from large perfect silicon crystals has been studied. It has been shown that the focusing effect makes it possible to reach an angular resolution better than 0.03″, which is about 0.01 of the width of a Bragg reflection. This circumstance allows a new ultraprecision neutron-spectrometry method based on the method of spin-echo small-angle neutron scattering in combination with Laue diffraction.

We measured the spatial splitting of a non-polarized neutron beam passed through a crystal under diffraction conditions in heterogeneous magnetic field (analog to the Stern-Gerlach effect) into two polarized components with opposite polarization. The measurements were carried out using Laue diffraction scheme, small gradients of the magnetic field and Bragg angles close to orthogonality θB=(78−82)∘. After a flight path in crystal of 21.6 cm a splitting of 4.1±0.1 cm was achieved (using a field gradient of ∼3 G/cm and a diffraction angle of 82∘). In the absence of a diffraction (crystal) but otherwise the same flight path and field gradient the spatial splitting would be ∼4⋅10−7 cm. From those we deduce an experimental amplification factor in the order of about ∼2⋅105tan2⁡θB due to the use of diffraction in crystals, which agrees with theory.

The effect of the neutron spin rotation at Laue diffraction in a weakly deformed noncentrosymmetric and transparent for the neutrons crystal has been theoretically described and experimentally investigated. This effect arises in the deformed crystal because of the curvature of the neutron trajectory in the crystal. A certain type of deformation leads to the escape outside the crystal of one of the two neutron waves excited at Laue diffraction. This two waves propagate in the crystal without a center of symmetry in electric fields with the opposite sign. In this case the spin of the remaining neutron wave will be rotating relative to the original direction due to the interaction of the magnetic moment of the moving neutron with the crystal's intracrystalline electric field. In a perfect undeformed crystal such spin rotation effect is absent. There is only a depolarization of the beam since both waves in opposite electric fields are present with the same amplitudes. A technique for controlled deformation of a perfect single crystal by creating a temperature gradient has been developed. Thus a new possibility to measure the electric fields which act on the neutron in noncentrosymmetric crystals has been realized. There also appeared a way to control these fields in experiments on the study of the neutron fundamental properties.

A crystal-di_raction experiment is discussed to test weak equivalence principle for neutrons. The idea of the experiment is based on essential magnification of any external force, acting on a neutron under di_raction at the Bragg angles close to the π/2 for Laue di_raction case. The enhancement factor from di_raction for neutron trajectory “curvature” in the crystal due to an external field can reach magnitudes of about ∼ (10 8 - 10 9 ) in comparison with a “free” neutron in the same field. Hence, the accuracy to measure the ratio of inertial to gravitational neutron masses can reach ∼ 10 -5 , that is about one order higher than best result.

Detailed study of a neutron Laue diffraction in a noncentrosymmetric crystal was carried out using a prototype of the experimental setup to measure the neutron electric dipole moment (nEDM) by Laue diffraction method (LDM). A new kind of spin rotation effect was observed for the first time. We attribute this effect to a difference of the two Bloch waves amplitudes in the crystal, which is caused by the presence of the definite small crystal deformation. In a revised scheme of the experiment, this effect could be exploited for a purposeful manipulation of the Bloch waves.

An essential magnification of an external force acting on a diffracting neutron for the Bragg angles θB close to the right one is observed. Any external action (caused by either crystal deformation or external force affected the neutron) results in a bend of the so called “Kato trajectories” inside the crystal and, for the case of a finite crystal, gives considerable variation of the intensities of both diffracted neutron beams (direct and reflected). It is shown that the magnification factor is proportional to tan2 (θb) and can reach (102−103) for Bragg angles surfficiently close to 90°.

The feasibility of an experiment to search for the neutron electric dipole moment (EDM) by Laue diffraction in crystals without a center of symmetry was tested. At the PF1A beam of the ILL reactor a record time delay of τ ≈2 ms for the passage of neutrons through a quartz crystal was reached for the (1 1 0) plane and diffraction angles equal to 88.5°. That corresponds to an effective neutron velocity in the crystal of 20 m/s, while the velocity of the incident neutron was 800 m/s. It was shown experimentally that the value τN 1/2 , determining the method's sensitivity, has a maximum for the Bragg angle equal to 86°. The results allow us to estimate the statistical sensitivity of the method for the neutron EDM. For the PF1B beam of the ILL reactor the sensitivity can reach ∼6×10 −25 e cm per day for the available quartz crystal.

Rotation of the spin of cold neutrons passing through a noncentrosymmetric single crystal is observed. This effect is caused by the Schwinger interaction of the magnetic moment of a moving neutron with the crystalline electric field in a noncentrosymmetric single crystal and depends both on the direction of neutron trajectory in the crystal and on its energy. It is shown that the characteristic magnitude of the effect for α-quartz is ≃(1–2)×10−4 rad/cm over a wide wavelength range (from 2.8 to 5.5 A) and is determined by the degree of beam monochromaticity [Δλ/λ=(2–5)×10−2 in our experiment]. This magnitude corresponds to an electric field of ≃(0.5–1)×105 V/cm acting on a neutron. The measured value agrees well with the theoretical calculation.

An experiment searching for the neutron electric dipole moment by measuring spin-rotations in a non-centrosymmetric crystal was carried out to investigate the statistical sensitivity and systematic effects of the method. The preliminary result of this experiment is d n = ( 2.5 ± 6.5 ) ⋅ 10 − 24 e ⋅ cm . The performance was essentially limited by the low luminosity of the prototype setup. With a dedicated setup and a large quartz crystal, the expected accuracy is ∼ 2 ⋅ 10 − 26 e ⋅ cm for 100 days of data collection.

A simple method for the relative measurement of the interplanar distances of high perfect crystals with a high precision is described. It is based on the comparison of the interplanar distances of two crystals using neutron transmission through one crystal and back reflection by the reference second crystal at Bragg angles close to 90 ∘ . The method allows us to measure the variation of the crystal interplanar distance Δ d relatively to the reference with the accuracy Δ d / d better than 10 - 7 .

An optical effect of a neutron spin rotation in the noncentrosymmetric quartz crystal was investigated. The effect was caused by the Schwinger interaction of the moving neutron with the strong electric field affects the neutron in noncentrosymmetric crystal. Value and sign of the effect depend on a deviation of the neutron energy from the Bragg one. We proposed to use the second crystal placed in parallel position to the main one to select the neutron with the given deviation parameter. It was shown that we could control and tune the value and sign of the electric field acting on the registered neutron by heating (or cooling) of the second crystal. The value of this field can reach ∼ 1 × 10 8 V/cm that gives us the real perspectives to improve essentially the present sensitivity to measure the neutron electric dipole moment (EDM) by the crystal diffraction technique.

The energy dependence of neutron refraction index in a perfect crystal for neutron energy, close to the Bragg ones, was studied. The resonance shape of this dependence with approximately the Darwin width was found. As a result, the value of deviation from the exact Bragg condition can change during the neutron time of flight through the accelerated crystal and so the refraction index and the velocity of outgoing neutron can change as well. Such new mechanism of neutron acceleration in the accelerating perfect crystal was proposed and found experimentally. This mechanism is march more effective then known one concerning with the neutron acceleration in the accelerating usual media.

Experiment for the search for the neutron electric dipole moment using Laue diffraction in a noncentrosymmetric crystal is proposed. The method is based on the effect of depolarization of the diffracted neutron beam due to interaction with an interplanar electric field of a noncentrosymmetric crystal. The value of this field can exceed ∼10 8 V/cm . An essential feature of the proposed Laue diffraction method is the possibility to increase more than by the order of value the time τ of neutron passage through the crystal and, accordingly, the time of interaction with the electric field using the Bragg angles close to π/2. The sensitivity of the method can be ∼10 −25 e cm / day for a really existing quartz crystal.