Neutron Spin Rotation at Laue Diffraction in a Weakly Deformed Transparent Crystal with No Center of Symmetry

Journal of Experimental and Theoretical Physics - The effect of neutron spin rotation at Laue diffraction in a weakly deformed neutron-transparent noncentrosymmetric crystal has been described...     

Depolarization of a neutron beam in Laue diffraction by a noncentrosymmetric crystal

The depolarization of a neutron beam executing Laue diffraction in a thick (～3.5 cm) noncentrosymmetric α-quartz crystal is observed. This effect was predicted by us earlier and suggested for measuring the electric dipole moment (EDM) of a neutron. The effect is due to an interaction of the magnetic moment of a moving neutron with a strong crystal electric field, as a result of which the neutron spin rotates in opposite directions for waves of two types excited in the crystal. The effect is studied for neutron diffraction by a system of crystallographic (110) planes at Bragg angles close to π/2, up to 87°. It is shown that, for a crystal of thickness L=3.5 cm, a direct beam initially polarized along the reciprocal lattice vector becomes depolarized upon diffraction, irrespective of the value of Bragg angle, whereas the beam polarized perpendicular to the diffraction plane retains its polarization. The Eτ value determining the sensitivity of the method to EDM is experimentally estimated.     

Direct measurement of the delay time for a neutron in a crystal in the case of the Laue diffraction

The dynamical Laue diffraction has been studied for a direct beam diffracted from a thin (～3.5 cm) α-quartz crystal at the Bragg angles close to 90°. It is shown that diffraction occurs at Bragg angles up to 87°. The time-of-flight method is used to measure the time of the neutron presence in the crystal under the diffraction conditions. The time delay for a scattered neutron inside the crystal predicted earlier for the Bragg angles close to 90° confirmed experimentally. The effective velocity of the neutron propagation in a crystal measured at the incident-neutron velocity of 810 m/s and the diffraction angle of 87° equals (43±1) m/s. The result obtained confirms the possibility of increasing, by an order of magnitude, the sensitivity of the diffraction method of determining the dipole moment of a neutron at Bragg angles close to 90° predicted earlier theoretically.     

Overcoming of the 12 reflectivity limit in Laue neutron diffraction

Experimental evidence for the overcoming of the 50% peak reflectivity limit in nuetron diffraction in the Laue geometry is presented. Peak reflectivity up to 75%, in spite of the neutron absorption, has been obtained with a bent germanium crystal. This effect has been explained by a simple model based on the dynamical theory of neutron diffraction and appears as a consequence of the elimination, due to a proper curvature, of the Pendellösung effect.     

Ultrasound effect on neutron Bragg diffraction in a perfect and deformed silicon single crystal

The features of neutron Bragg diffraction in a perfect and bent (deformed) silicon single crystal have been studied under ultrasound excitation. In contrast to a perfect crystal where an increase in the diffraction intensity has been observed with an increase in the ultrasound wave’s amplitude, in a deformed silicon crystal the intensity sharply decreases (two times) already at small voltages on a piezoelectric transducer. The depth and position of minima of the total intensity depend on the ultrasound wave’s amplitude and the bending radius of a crystal. To explain the observed effects the modified Penning-Polder-Kato model has been successfully used, in which the role of ultrasound is reduced to the formation of resonance transitions of imaging points between different sheets of dispersion surface. Experimental proofs of validity of the used model are presented. Estimations of the probabilities of one- and multiphonon scattering processes obtained from experimental data have a good agreement with theoretical ones.     

Elasticity effects on domain coarsening of the lamellar-gyroid transition observed in a nonionic surfactant system

The coarsening process of the gyroid phase of a nonionic surfactant system is investigated by time resolved small angle neutron scattering (SANS) and small angle neutron Laue diffraction techniques. The time evolution of SANS patterns shows anomalous coarsening of the gyroid domains. The observed Laue spot from a gyroid domain becomes elongated along the radial direction with the elapse of time and at a certain time the elongated spot is split into two spots. The results can be interpreted as follows. During the coarsening process, mismatch of the lattice orientation at the domain boundary brings strong stress to the gyroid domain, resulting in the distortion of the domain. The stored stress in the domain finally brings splitting of the gyroid domain. The elastic and fragile nature of the gyroid domains composed of the "soft matter" is responsible for the anomalous coarsening.     

晶体X射线劳厄衍射分束特性研究

本文基于X射线衍射动力学分析了劳厄晶体的分束特性,模拟了晶体吸收和入射光角发散对于透射光和衍射光摇摆曲线的影响,定量给出晶体衍射面内角调节范围和晶体加工厚度对于劳厄衍射分束比的调制.在实验中,采用分析晶体和分束晶体的消色散配置限制入射光角发散的影响,实现300μm厚Si(220)晶体面内角调节劳厄衍射分束的精确测量,并得到300μm, 400μm和500μm厚度Si晶体分束比的调节范围,实现了透射光和衍射光强度的定量调制.     

Dislocation-based plasticity model and micro-beam Laue diffraction analysis of polycrystalline Ni foil: A forward prediction

A physically-based, rate and length-scale dependent strain gradient crystal plasticity framework was employed to simulate the polycrystalline plastic deformation at the microscopic level in a large-grained, commercially pure Ni sample. The latter was characterised in terms of the grain morphology and orientation (in the bulk) by micro-beam Laue diffraction experiments carried out on beamline B16 at Diamond Light Source. The corresponding finite element model was developed using a grain-based mesh with the specific grain orientation assignment appropriate for the sample considered. Sample stretching to 2% plastic strain was simulated, and a post-processor was developed to extract the information about the local lattice misorientation (curvature), enabling forward-prediction of the Laue diffraction patterns. The ‘streaking’ phenomenon of the Laue spots (anisotropic broadening of two-dimensional (2D) diffraction peaks observed on the 2D detector) was correctly captured by the simulation, as constructed by direct superposition of reflections from different integration points within the diffraction gauge volume. Good agreement was found between the images collected from experiments and simulation patterns at various positions in the sample.     

Control of the parameters of a beam of thermal neutrons

The reflection of thermal neutron beams from a quartz single crystal was investigated in the Laue geometry under the external influences. The controllability of a neutron beam in space and time is analyzed and its parameters are estimated (relative maximum intensity, the angular and energy distribution of obtained beams etc.).     

Structure and physical properties of layered double perovskite NdBaCo2O5.50 + δ (δ ≈ 0.25)

Magnetic, electric, and elastic properties of the crystal and magnetic structure of double layered perovskite NdBaCo₂O_{5.50 + δ} are studied by the neutron diffraction method at various temperatures. The data are analyzed using two models of crystal structure. In the first model, the sample consists of two crystal-structure phases with ordered and disordered arrangements of oxygen vacancies. In the second model, a new crystal-structure phase is formed in this compound, which is characterized by ordering of oxygen vacancies in the plane of the rare-earth ion in the 1c crystallographic position (0, 0, 1/2) of space group Pmmm. Two crystal-structure models correspond to different types of magnetic ordering (a mixture of a ferromagnetic phase and a G-type antiferromagnetic phase is presumed in the two-phase crystal-structure model, while a canted antiferromagnetic structure is presumed in the one-phase crystal structure model). The behavior of electric and elastic parameters is better described in the first model, while neutron diffraction studies are in better agreement with the second model.     

劳厄对晶体衍射的发现

介绍了劳厄提出晶体衍射思想的科学背景及当时的实验过程,并探讨在劳厄发现晶体衍射的过程中其科学思想的形成及X射线晶体衍射的发现带给我们的启示及影响．     

吸收限附近GaAs在劳厄情况下的荧光溢出

利用同步辐射光源，在Ga和As的K吸收限之间调节入射X射线的能量时，在对称劳厄情况下，GaAs的(200)衍射峰附近可观测到从GaAs的入射面出射的Ga的K系荧光X射线.当入射X射线的能量改变时，荧光曲线的非对称性会发生变化，变化趋势与相应的对称布喇格情况相类似.但是，劳厄情况下的变化不能解释为晶体内部X射线驻波的波节面相对于GaAs(200)格子面的移动.在劳厄情况下，X射线驻波的振幅随入射角的变化与结构因子的相位密切相关，因此结构因子的相位变化也会导致荧光曲线的非对称性变化.在假设原子的荧光溢出与该原 关键词：     

Electric dipole moment of the neutron in the electric field of a crystal

The effect of the weak interaction on the diffraction measurement of the electric dipole moment of neutrons moving in crystal electric fields has been analyzed. It has been shown that the interference of the Schwinger interaction with the weak interaction field imposes restrictions on the measured electric dipole moment of the neutron.     

Peculiarities of Laue Diffraction of Neutrons in Strongly Absorbing Crystals

Journal of Experimental and Theoretical Physics - Well-known Kato’s theory of the Laue diffraction of spherical X-ray waves is generalized to the case of the neutron diffraction in strongly...     

Accuracy of stress measurement by Laue microdiffraction (Laue‐DIC method): the influence of image noise,calibration errors and spot number

Laue microdiffraction, available at several synchrotron radiation facilities, is well suited for measuring the intragranular stress field in deformed materials thanks to the achievable submicrometer beam size. The traditional method for extracting elastic strain (and hence stress) and lattice orientation from a microdiffraction image relies on fitting each Laue spot with an analytical function to estimate the peak position on the detector screen. The method is thus limited to spots exhibiting ellipsoidal shapes, thereby impeding the study of specimens plastically deformed. To overcome this difficulty, the so‐called Laue‐DIC method introduces digital image correlation (DIC) for the evaluation of the relative positions of spots, which can thus be of any shape. This paper is dedicated to evaluating the accuracy of this Laue‐DIC method. First, a simple image noise model is established and verified on the data acquired at beamline BM32 of the European Synchrotron Radiation Facility. Then, the effect of image noise on errors on spot displacement measured by DIC is evaluated by Monte Carlo simulation. Finally, the combined effect of the image noise, calibration errors and the number of Laue spots used for data treatment is investigated. Results in terms of the uncertainty of stress measurement are provided, and various error regimes are identified.     

Anomalous behavior of the dispersion of a neutron transmitting through a crystal at nearly Bragg energies

The features of the propagation of a neutron through a crystal at nearly Bragg energies has been studied within the framework of the preparation of an experiment on the search for the electric dipole moment of a neutron by the crystal diffraction method. The time of passage of the neutron through the crystal has been studied as a function of the deviation from the Bragg condition. The anomalous behavior of the dispersion of the neutron, i.e., the energy dependence of its average velocity, has been observed. It has been shown that the derivative dv/dE for the diffracting neutron at nearly Bragg energies can be three or four orders of magnitude larger than this derivative for a free neutron. This opens new possibilities in precision neutron spectroscopy.     

Linear effect of doubling of the laser pulse repetition rate in the laue geometry of bragg diffraction in a photonic crystal

It has been theoretically shown that, during Bragg diffraction of a picosecond laser pulse in the Laue geometry in a linear photonic crystal, the pulse, entering the crystal structure, may be split into two transmitted and two diffracted pulses. The time interval between these pulses can be controlled by varying the crystal thickness and the modulation depth of the refractive index.     

ZnS晶体3C⇔2H结构转变的LAUE衍射图中“奇异点”的标定

在ZnS晶体3C⇔2H结构转变的X—射线Laue衍射分析中,为了解释一维无序造成的异常衍射现象,本文推导了Laue衍射图曲线晶带的“奇异点”计算公式。并应用此公式,计算了ZnSLaue衍射照片上数条晶带上的“奇异点”,计算值与实验值完全吻合。另外,本文还对“奇异点”的形成、特点、标定的意义以及计算公式适用范围进行了讨论。     

Effect of the Temperature Gradient on the X-ray Diffraction Spectrum of a Quartz Crystal

The spectra of X-ray diffraction from the reflecting atomic plane (1 0 1? 1) of a quartz single crystal are studied in Laue geometry under the action of temperature gradient on a BDER-KI-11K spectrometer with a resolution of 300 eV on the Am241 line of 17.74 keV. The temperature gradient leads to an increase in the intensity of the diffracted beam depending on the heating temperature. It is shown that the intensity of X-ray diffraction in Laue geometry may increase at a temperature gradient of 250°C/cm by two orders of magnitude in comparison with the uniform temperature state of the crystal. The rocking curve of the reflected beam is obtained at a fixed observation angle of 6° and a specified temperature gradient. It is demonstrated that the intensity of the reflected beam increases with increasing temperature gradient (to a certain value), while the spectral width of the reflection line remains constant and is governed by the energy resolution of the spectrometer. A further growth in the temperature gradient leads to an increase in the spectral width of the reflection line with decreasing intensity of the reflected beam.     

Verification of the weak equivalence principle with Laue diffracting neutrons: Test experiment

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.