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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.

Investigations of the spatial resolution of a setup for verification of the equivalence of inertial and gravitational masses of a neutron by the method of diffraction in a perfect crystal have been performed. Tests were conducted at Bragg angles of 74°–82°. A decrease in spatial resolution at Bragg angles >78° is detected.

A new mechanism of neutron acceleration is studied experimentally in detail for cold neutrons passing through the accelerated perfect crystal with the energies close to the Bragg one. The effect arises due to the following reason. The crystal refraction index (neutron–crystal interaction potential) for neutron in the vicinity of the Bragg resonance sharply depends on the parameter of deviation from the exact Bragg condition, i.e. on the crystal–neutron relative velocity. Therefore the neutrons enter into the accelerated crystal with one neutron–crystal interaction potential and exit with the other. Neutron kinetic energy cannot vary inside the crystal due to its homogeneity. So, after passage through such a crystal, neutrons will be accelerated or decelerated because of the different energy change at the entrance and exit crystal boundaries.

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 describe the structure design and present the results of experimental testing of a birefringent magnetic neutron prisms for spin-echo small-angle neutron scattering (SESANS). The SESANS setup, equipped with perfect single crystals for measuring diffraction-enhanced spin interference effects, must possess unprecedented sensitivity with respect to small external actions on a neutron and is intended for use in experiments for checking the neutron electroneutrality.

We propose a novel experiment to test the weak equivalence principle (WEP) for the Laue diffracting neutron. Our experiment is based on an essential magnification of an external affect on neutron diffracting by Laue for the Bragg angles close to the right one in couple with additional enhancement factor which exists due to the delay of the Laue diffracting neutron at such Bragg angles. This enhancement phenomena is proposed to be utilized for measuring the force which deviates from zero if WEP is violated. The accuracy of measuring inertial to gravitational neutron masses ratio for the introduced setup can reach ∼10−5, which is more than one order superior to the best present-day result.

A direct experimental observation of the anomalous absorption of neutrons undergoing Laue diffraction in a highly perfect silicon single crystal of size about 200 mm at Bragg angles close to π/2 is reported. It is shown that, in the case of diffraction at the (220) plane, the neutron absorption length may be several meters, which is nearly one order of magnitude longer than the mean absorption length for neutrons of the same wavelength. This circumstance makes it possible to study effects accompanying Laue diffraction at Bragg angles of up to 88° and a crystal size of about 200 mm.

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.

An experiment using a prototype setup to search for the neutron electric dipole moment by measuring spin-rotation in a non-centrosymmetric crystal (quartz) was carried out to investigate statistical sensitivity and systematic effects of the method. It has been demonstrated that the concept of the method works. The preliminary result of the experiment is $d_{\rm n}=(2.5\pm 6.5)\cdot 10^{-24}$ e$\cdot $cm. The experiment showed that an accuracy of $\sim 2.5\cdot 10^{-26}$ e$\cdot $cm can be obtained in 100 days data taking, using available quartz crystals and neutron beams., 13 pages, 4 figures

The essential magnification of an external affect on neutron diffracting by Laue for the Bragg angles θ B close to right one has been experimentally observed. The factor of diffraction enhancement for the neutron trajectory “curvature” due to external field is proportional to tan 2 θ B and can reach magnitude ∼ 10 8 – 10 9 in comparison with a free neutron. The new method to measure a neutron electric charge and the ratio of inertial to gravitational masses has been proposed. The estimations have shown a feasibility to improve the accuracy of a neutron electric charge measurement by about two orders of magnitude in comparison with the current value and measure the ratio of inertial to gravitational masses with the accuracy about σ ( m i / m G ) ∼ 10 - 6 .

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°.

A new way is proposed and investigated for observing and fine tuning a neutron spin rotation effect caused by the Schwinger interaction of the moving neutron with the strong interplanar electric field of the noncentrosymmetric quartz crystal. By that we have got an opportunity to control the electric field acting on neutron. The value and sign of this field depend on the deviation of a neutron energy from the Bragg one. We used a second crystal parallel to the main one for selection of the neutrons with the given deviation parameter. The possibility to control the electric field acting on the registered neutrons has been realized by heating (or cooling) the second crystal. Observed effects give a real prospects to improve essentially the scheme and sensitivity of the experiment for a search for neutron electric dipole moment (EDM) using the crystal diffraction technique.

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.

First observation of new effects was carried out using the set-up created for searching for a neutron electric dipole moment (EDM) by a crystal-diffraction method. For the first time the neutron dynamical Laue diffraction for the Bragg angles close to a right angle (up to 87°) was studied, using the direct diffraction beam and a thick (∼3.5-cm) crystal. The effect of an essential time delay of diffracting neutrons inside the crystal for Bragg angles close to 90° was experimentally observed, using a time-of-flight method. The phenomenon of neutron-beam depolarization was first experimentally observed for the case of Laue diffraction in a noncentrosymmetric α-quartz crystal. It is experimentally proved that the interplanar electric field, affecting a neutron in a crystal, maintains its value up to Bragg angles equal to 87°. These results confirm the opportunity to increase by more than an order of magnitude the sensitivity of the method to the neutron EDM, using the diffraction angles close to 90°, and give a real prospect to exceed the sensitivity of the magnetic resonance method, using ultra-cold neutrons.

Possible future progress of the crystal-diffraction neutron electric dipole moment search experiment is discussed. A storage modification of the experiment is proposed. It is demonstrated that sensitivity of the method can be a few 10 −27 e cm for the BSO crystal with the size 10×10×10 cm 3 and expected luminosity of European Spallation Source (ESS).

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.

In the present work we report the analysis of spin effects for neutrons diffracted by a noncentrosymmetric crystal in a Laue diffraction scheme. New method of a search for neutron electric dipole moment is proposed. It is based on the predicted new effect of depolarization of the diffracted neutron beams (direct and reflected) due to neutron interaction with the strong interplanar electric field (up to 10 9 V/cm).