High-resolution Neutron Diffractometer Research Articles

High-Resolution Three-Axis Neutron Diffractometer for Microstructure Investigations of Polycrystalline Materials

Recently, focusing 3-axis diffractometer set-up equipped with the bent perfect crystal (BPC) monochromator and analyzer which has offered the sensitivity in determination of strains Δd/d < 10−4 in polycrystalline materials, has been introduced. The resolution determined by FWHM of the diffraction profiles is about one order of magnitude higher with respect to that of conventional 2-axis neutron strain/stress scanners. Therefore, the new set-up also offers possibility of line profile analysis for relatively large irradiated gauge volumes and reasonable counting times, because the 3-axis set-up exploits focusing in real and momentum space simultaneously. As it is demonstrated on several samples, the 3-axis diffractometer can be successfully used in the strain/stress measurements on samples exposed to an external load, studies of diffraction profile affected by plastic deformation, determination of phases having very close values of the lattice spacings etc. The analysis is carried out by rocking the BPC analyzer and the neutron signal is registered by a point detector.

Determination of neutron capture cross section of 164Dy (n,)165 Dy reaction at 0.0334 eV using TRIGA reactor

In this study, experimental neutron capture cross section for the reaction 164Dy(n, γ )165Dy at 0.0334 eV was measured for the first time using monochromatic neutrons coming out of a high resolution neutron diffractometer at the BAEC TRIGA Research Reactor (BTRR), Dhaka, Bangladesh. The 197Au(n, γ )198Au monitor reaction was used to determine the effective neutron flux. The activities of the irradiated target and monitors were measured nondestructively using the HPGe detector coupled with the digital gamma-ray spectrometry system. The full energy photo peak detection efficiency curve of the detector was constructed using standard gamma-ray emitting sources and this curve was used to acquire efficiencies of the detector at different required energies. Using the well-known neutron activation formula, the neutron capture cross-sections of 164Dy(n, γ )165Dy reaction were obtained 2322 ± 140 barn at 0.0334 eV. The cross section at 0.0334 eV is 4.3%, 4.5% and 3.15% higher than the evaluated values extracted from the ENDF/B-VII.1, ROSFOND and JENDL-4.0, respectively.

An alternative neutron diffractometer performance for strain/stress measurements

An alternative neutron diffractometer performance, which documents the feasibility of using a high-resolution three-axis neutron diffractometer for elastic and plastic deformation studies of bulk metallic polycrystalline samples, is presented. Contrary to the conventional double-axis setting, the suggested alternative consists of an unconventional three-axis set-up employing a bent perfect crystal monochromator and an analyzer with a polycrystalline sample in between. Though the alternative is, for measurements, much more time-consuming, its sensitivity to the change of the diffraction angle of the sample is, however, substantially higher and permits also plastic deformation studies on the basis of analysis of the diffraction line profiles. Moreover, much larger widths (up to 10 mm) of the irradiated gauge volumes can be investigated when just slightly affecting the angular resolution properties of the experimental setting.

Real time observation of martensite transformation for a 0.4C low alloyed steel by neutron diffraction

A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium-carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during quenching with and without the ausforming process. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. After ausforming, the data reveal that lattice parameters are larger in austenite whereas smaller in martensite compared with those in the non-ausformed case, which is ascribed to the introduced dislocations. Thus, the lattice defects affect the lattice parameter during martensite transformation. Ausforming also slightly raises the Ms temperature and increases the amount of retained austenite at room temperature as a result of different dislocation densities. The cutting-edge operant quantitative measurements with neutron diffraction for steel production is demonstrated.

Real Time Observation of Martensite Transformation for a 0.4C Low Alloyed Steel by Neutron Diffraction

A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during fast cooling and during the ausforming process. The hkl diffraction intensity of austenite increased at the beginning of transformation due to the primary extinction effect. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. Ausforming slightly increases the Ms temperature, the amount of retained austenite at RT and the austenite lattice parameter. The dislocation densities in martensite and the retained austenite estimated using the convolutional multiple whole profile fitting method increase by ausforming.

Refinement of the Atomic and Magnetic Structures of Solid Solutions BaFe12 – xInxO19 (x = 0.1–1.2) by the Neutron Diffraction Method

Structural investigations of solid solutions of BaFe12 – xInxO19 barium ferrites partially substituted with indium ions (x = 0.1–1.2) are carried out via the neutron diffraction method. Experimental investigations of ceramic samples are performed at room temperature using a high-resolution neutron diffractometer that allows precise information about changes in the crystal and magnetic structures, as well as microstructural parameters, to be obtained. Refinement of the crystal structure of the composition BaFe12 – xInxO19 is carried out in the framework of two space groups P63/mmc and Р63mc. Solid solutions of barium ferrites retain the hexagonal crystal-structure type in the entire investigated concentration range. Their ferrimagnetic structure is well described by Gorter’s model where magnetic moments are ordered along the c axis. Spontaneous polarization is revealed in barium hexaferrites partially substituted with indium ions. The total magnetic moment per formula unit decreases as the amount of diamagnetic In ions is increased. An increase in microstrains in the crystallites with increasing amount of In ions is explained by increasing disorder of the system because of the statistical distribution of diamagnetic ions in magnetic sublattices.

High-Resolution Neutron Diffractometer Based on the IN-06 Pulsed Neutron Source at the Institute for Nuclear Research, Russian Academy of Sciences

A high-resolution neutron diffractometer has been fabricated on the basis of an IN-06 pulsed neutron source at the Institute for Nuclear Research, Russian Academy of Sciences. The diffractometer incorporates two blocks of detectors with helium neutron counters and time-of-flight (TOF) focusing at scattering angles of 156°–165°. A block of new-type high-efficiency scintillation detectors of thermal neutrons based on a ZnS(Ag)/LiF scintillator and silicon photomultipliers with TOF focusing is developed and tested. Test measurements are performed, and the diffractometer resolution is estimated. The diffraction pattern of nonmagnetic NiCrAl alloy is measured and used to determine the phase composition by means of the Rietveld method. It is demonstrated that the given setup can be applied to phase analysis.

High resolution neutron diffractometer HRND at research reactor CMRR

The high resolution neutron diffractometer HRND is located at the 20 MW China Mianyang Research Reactor (CMRR), which is a neutron powder diffractometer especially dedicated to crystal and magnetic structure studies for polycrystalline powder samples. A vertical focusing Ge (511) monochromator produce a monochromatic neutron beam with a wavelength of 1.885 Å at a fixed take-off angle of 120̂. An array of 64 equidistant 3He filled proportional counters can acquire diffraction patterns with a large-scale diffraction angle range over 160̂. As all the Soller slit collimators of HRND have a collimation angle of 10′ and the monochromator has an average mosaicity of 0.359̂, HRND obtains a best resolution of about 1.6\ extperthousand based on experiments, which makes the resolution of HRND can compete with the mainstream-level high resolution neutron powder diffractometers in the world. Equipped with a cryostat and a furnace, HRND allows structural characterization in an extremely broad temperature range. The details of the configuration and performance of the instrument are reported along with its specifications and performance assessments in the present paper.

Performance improvement of the high resolution neutron diffractometer at CAEP with Geant4 simulation

The newly-built high resolution neutron diffractometer (HRND) at China Academy of Engineering Physics (CAEP) could not acquire high-quality diffraction patterns. In order to solve the problem, the present work introduces the Monte Carlo method based software called Geant4 which is rarely applied in the field of neutron diffraction. The geometrical structure of HRND has been structured by Geant4, thus simulation results can not only re-display the problems of HRND but help to solve such problems as well. According to the simulation results, some effective measures have been carried out to obtain higher instrument performance. It is found that the performance of HRND is improved eventually after new experimental diffraction patterns are acquired.

Neutron diffraction analysis of the microstructure of dispersion-hardening steels

Neutron diffraction was employed in order to determine microdeformations in samples of stainless austenitic dispersion-hardened steels subjected to the action of high temperatures (to 700°С) during different times (up to 12 h). Experiments were conducted on a high-resolution neutron diffractometer using the timeof- flight method. The analysis performed showed systematic changes in the parameters and microdeformations of the crystal lattice. The high level of the diffractometer resolving power made it possible to reveal some important additional details of the microstructure of dispersion-hardened steels as compared to the results obtained earlier on a diffractometer with monochromatic neutron beam.

Diagnosis of the Storage Aging of a Commercial Cell with Neutron Powder Diffraction

Neutron diffraction is an alternative tool to study the structural changes of a commercial lithium ion cell in operando due to its high penetration, low interaction with matter, and sensitive to low atomic number elements. High resolution neutron diffractometer (Echidna at ANSTO) and high intensity neutron powder diffractometer (Wombat at ANSTO) were used in this study to investigate the structures of a fresh and storage aged commercial 18650 cells (comprised with LiNi0.5Mn0.3Co0.2O2 (NMC)/Li1.1Mn1.9O4 (LMO) composite cathode and graphite anode) and their structural changes upon charge/discharge cycling. It was found that the storage capacity fade increases significantly with increasing storage temperature after 6 months storage. The capacity fades of the cells stored at 0, 25, 50, 75, and 100% DOD are 9.9, 17.5, 7.5, 3.6, and 0.7 %, respectively, after stored at 60oC for 6 months.Figure 1 shows the typical high resolution NPD pattern and its refinement of a fresh cell, while Table 1 lists the results of Rietveld refinement for the NPD patterns of the fresh and aged cells at their the fully discharged and charged states after been stored at 0, 25, and 50 %DOD at 60oC for 6 months. It can be found that the aged cells manifest similar lattice parameters of LMO and NMC at their fully charged state as those of fresh cell, respectively. However, the aged cells show smaller lattice parameter of LMO than that of fresh one and the value decreases with decreasing DOD of storage. That suggests the cell stored at 0% DOD has the most severe structure change in LMO among the samples stored at 60oC for 6 months. From the in-situ 2D ND patterns of the fresh and aged cells collected every 5 minutes with Wombat upon cycling at 215 mA within 2.75 and 4.2 V, shown in Fig. 2, the variation in lattice parameters of LMO and NMC can be determined. The values of the parameters at their charged and discharged states obtained from sequential Rietveld refinement are similar as those shown in Table 1. From the intensity changes of LMO 222 plane after storage for 6 months, it can be found that the sample stored at 0% DOD shows higher LMO loss than other stored samples, which can also be revealed from the abrupt change in lattice parameter of the sample at 4.06 V upon charge/discharge cycling, while linear change in parameter are observed in case of other samples. Aged sample stored at 25% DOD shows lower intensity of LiC6 001 plane manifests the sample has higher lithium loss of inventory (LLI) than others, which can also be revealed from the changes after storage in lattice parameters of NMC at discharged state, shown in Table 1, and intensity of NMC 003 plane at discharged state shown in Fig. 2. These are in consistent with the results obtained from ICA study for the charge/discharge curves and post-mortem studies. The results suggest that the capacity losses of the samples stored at 0 and 25% DOD can be attributed to loss of LMO and LLI, whereas samples stored at depth of discharge higher than 50% DOD can be caused by loss of LLI only. Figure 1

High-resolution neutron powder diffractometer SPODI at research reactor FRM II

SPODI is a high-resolution thermal neutron diffractometer at the research reactor Heinz Maier-Leibnitz (FRM II) especially dedicated to structural studies of complex systems. Unique features like a very large monochromator take-off angle of 155° and a 5 m monochromator–sample distance in its standard configuration achieve both high-resolution and a good profile shape for a broad scattering angle range. Two dimensional data are collected by an array of 80 vertical position sensitive 3He detectors. SPODI is well suited for studies of complex structural and magnetic order and disorder phenomena at non-ambient conditions. In addition to standard sample environment facilities (cryostats, furnaces, magnet) specific devices (rotatable load frame, cell for electric fields, multichannel potentiostat) were developed. Thus the characterisation of functional materials at in-operando conditions can be achieved. In this contribution the details of the design and present performance of the instrument are reported along with its specifications. A new concept for data reduction using a 2 θ dependent variable height for the intensity integration along the Debye–Scherrer lines is introduced.

Neutron diffraction study of diffuse scattering in Cu 2− δSe superionic compounds

Crystal structure and short-range order in Cu 2− δ Se compounds were studied in superionic and non-superionic phases using high-resolution neutron diffractometer Echidna at ANSTO. In diffraction patterns of β-Cu 1.98Se (ordered phase at ambient T), both Bragg peaks and diffuse background change sharply through the β → α structural phase transition at T = 414 K during heating. In case of α-Cu 1.75Se (disordered superionic phase at ambient T) the changes are monotonic, showing gradual shifts of Bragg peaks and increased intensity of the diffuse background as a function of temperature. On cooling, both compounds undergo a β → β′ transformation. Diffuse scattering in the α-phase shows an oscillating dependence on wavevector, with broad peaks centred at Q ∼ 3, 5.5 and 8 Å −1. The measurements taken in energy dispersive mode show that the oscillating diffuse background arises from correlated thermal displacements of the ions. Diffuse scattering is higher for compositions close to stoichiometry and increases with temperature. Theoretical calculations show that the increase in diffuse intensity both with temperature and Cu content is related to correlated thermal vibrations of Se and Cu atoms, with Se–Cu( 8c, 32f) and Cu( 8c)–Cu( 8c) correlations being the most important.

High-Resolution Neutron Diffraction for Nondestructive Analysis of Residual Stresses in Polycrystalline Materials

The performance of an unconventional high-resolution neutron diffractometer using Bragg diffraction optics that can be efficiently employed in strain/stress diffractometers are reported. Presented results demonstrate their experimental abilities for powder diffraction, namely for residual strain/stress measurements. In addition to the macrostrain scanning capability, the device can also be used for microstrain/stress studies by suitable analysis of the diffraction profiles. Two examples of the strain measurements are presented.

Conceptual design of a macromolecular neutron diffractometer (MaNDi) for the SNS

This paper describes the design criteria, calculations and simulations for a high-resolution macromolecular neutron diffractometer (MaNDi) for the Spallation Neutron Source (SNS). MaNDi is optimized to achieve 1.5 Å resolution from crystals of 0.1–1 mm3with lattice repeats in the range of 150 Å. It was determined that locating MaNDi on a decoupled hydrogen moderator beamline with a curved guide will provide data of higher resolution and higher signal-to-noise than a coupled hydrogen moderator at the SNS. In addition, for an instrument with an initial flight path of 24 m at the 60 Hz source and a wavelength bandwidth of Δλ≃ 2.7 Å, bandwidth selection disk choppers can shift the wavelength range higher or lower for different experiments. With a wavelength range of 1.5–4.2 Å anddmin= 2.0 Å, simulations predict experiment duration times of 1–7 d, which is expected to revolutionize neutron macromolecular crystallography (NMC) for applications in the fields of structural biology, enzymology and computational chemistry.

Investigation of Residual Stresses in a Bimetallic Stainless Steel-Zirconium Adapter by Neutron Diffraction

In this paper we present the results of residual stress measurements in a bimetallic stainless steel –zirconium adapter, which is used in some structures of RBMK reactor channels. The stresses in this component arise due to various manufacturing processes and the thermal expansion factor mismatch between the two alloys. The residual stress distribution in stainless steel was investigated. The residual stresses on three different cross sections were measured. The experiments were carried out on High Resolution Fourier Diffractometer (HRFD) and Fourier stress Diffractometer (FSD) at the pulsed reactor IBR-2 (Dubna, Russia) and on the high-resolution neutron diffractometer at power reactor LVR 15 (NPI, Rez, Czech Republic).

High-resolution and high-intensity neutron diffractometer with linear position-sensitive detector

The characteristics of a neutron diffractometer using a 3 He one-dimensional position-sensitive detector (PSD) with delay line readout, a 200 (length) × 100 (height) mm 2 active window and 2.5 mm spatial resolution have been studied and compared with those of the High-Resolution Powder Diffractometer (HRPD) of KAERI with 32 3 He conventional tube (∅50 mm) detectors and Soller collimators (10′) before detectors. For the sample to PSD distance R=1200 mm , the PSD subtends 8° angle of 2 θ and provides the resolution and the peak-to-background ratio close to that for HRPD. Time for scanning (with the same statistics) of a 0–160° interval is about 1.6 times longer and the multi-PSD system providing efficiency about 10 times higher than HRPD is proposed. Because of the small angle subtended by the PSD, the parasitic peaks from the sample environment are eliminated and operation without an oscillating radial collimator is possible. Additionally, the proposed diffractometer has an advantage for small samples.

High resolution neutron protein crystallography. Hydrogen and hydration in proteins

Abstract Neutron diffraction provides an experimental method of directly locating hydrogen atoms in proteins, and the development of the neutron imaging plate (NIP) became a breakthrough event in neutron protein crystallography. The general features of the NIP are reviewed. A high resolution neutron diffractometer dedicated to biological macromolecules (BIX-3) with the NIP has been constructed at Japan Atomic Energy Research Institute and this has enabled 1.5 Å resolution structural analyses of several proteins to be carried out. The specifications of BIX-3 and LADI (a quasi-Laue type diffractometer installed in the Institut Laue-Langevin) are compared. The crystal structures of myoglobin, wild type rubredoxin and a mutant of rubredoxin have been carried out using BIX-3. From these studies, several topics, such as the location of hydrogen bonds and certain acidic hydrogen atoms, the identification of methyl hydrogen atoms, details of H/D exchange and dynamical behavior of hydration structures have been investigated, and important information has been extracted from the structural results. Finally, a systematic procedure to grow large single crystals of proteins or nucleic acids is described.

High-resolution diffraction using Larmor precession of polarized neutrons

A new Larmor precession device, consisting of two separate precession modules, is introduced. It operates as a high-resolution neutron diffractometer, without the need for a highly collimated beam, necessary in conventional high-resolution neutron diffraction. The same instrument operates in different modes as an effective small-angle scattering device or accurately determines the line profile, the lattice plane orientation or the angular spread in crystal orientations. A dramatic intensity gain can be obtained in all applications discussed, compared with the conventional analogues, owing to the possibility to use a relaxed wavelength and angular resolution. Experiments in the high-resolution diffraction mode on Si and Al are discussed.

Neutron diffraction study of the ordered structures of nonstoichiometric titanium carbide

The ordered structures and phase transitions in TiC 0.62 and TiC 0.59 are investigated on the high resolution neutron diffractometer. It is established, that low-temperature trigonal δ″(sp.gr. R 3 ̄ m or sp.gr. P3 121) and high-temperature cubic δ′(sp.gr. Fd3m) ordered structures, according to the temperature, exist in the investigated carbide samples. Under heating, the sample TiC 0.62 experiences the order-order (δ″( R 3 ̄ m )→δ′(Fd3m)) phase transition at 770°C and then, the order-disorder ((δ′(Fd3m)→δ(Fm3m)) phase transition at 790°C.