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Neutron optics exploits the similarities between the quantum-mechanical description of neutron propagation and scattering and the equivalent equations of light propagation used in classical optics. One of its most exciting possibilities relies on neutron waveguiding in a similar way an optical fibre, or a waveguide, does with light. This possibility was proposed by De Wames and Sinha, in 1973 and experimentally demonstrated by Kumakhov, in 1992. This paper reviews the work in the author's PhD thesis, where it has been proposed an original rigorous mathematical characterization of how a thermal neutron beam impinging a waveguide extincts, gives rise to propagation modes and propagates (including its escape via tunnelling effect). This new mathematical characterization led to the development of an original efficient algorithm never implemented before for simulation including holography. The final goal is to identify critical parameters to improve the design of waveguiding devices. The main challenge is that, when one simulates waveguides with transverse dimensions (aperture) orders of magnitude higher than the neutron wavelength, it involves complex integral equations with a huge volume of data to handle and compute. [ABSTRACT FROM AUTHOR]

We present calculations of interferograms (interference patterns) of one or multiple spiral phase plates that would be observed with a perfect crystal neutron interferometer of Mach–Zehnder type. A spiral phase plate (SPP) in one of the two coherent beam paths produces a twist in the phase front and thus a vortex beam with intrinsic angular momentum, which in the case of neutrons should be observed as a characteristic interference pattern that appears complementary to each other in both detectors behind the interferometer. Adding additional SPPs in one beam path of the interferometer yield interference patterns similar to that of a single SPP but only due to the cumulative step height. All simulated interferograms have been calculated on the basis of dynamical neutron diffraction without any assumption of a neutron orbital angular momentum and show very convincing agreement with experimental results from the literature, see e.g. (C. W. Clark, R. Barankov, M. G. Huber, M. Arif, D. G. Cory, and D. A. Pushin, "Controlling neutron orbital angular momentum," Nature, vol. 525, pp. 504–506, 2015). In particular, this clarifies, that the cited experiments do not give evidence of the quantization of interactions caused by a twist of the phase front of a neutron wave in the interferometer and thus no evidence for the effect of a neutron orbital angular momentum. [ABSTRACT FROM AUTHOR]

The neutron flux is a crucial factor for neutron scattering measurements, especially for compact sources. Among various neutron optics, grazing‐incidence focusing mirrors have been developed to give a significant increase in the neutron flux on a sample owing to their great potential for collecting neutrons in small‐angle neutron scattering (SANS) instruments. Focusing mirrors with a supermirror coating can be nested to collect a neutron beam with large divergence. Nested conical integrated assembly technology is employed to manufacture nested focusing mirrors. This study describes the design of ten‐shell nested fully annular quasi‐ellipsoidal focusing mirrors with an m = 3 Ni/Ti supermirror coating to produce enough neutrons on a sample under the premise of satisfying the specified minimum wavevector transfer Q. For fully annular focusing mirrors, the neutron current received by a sample from the entire annular focusing neutron beam is more relevant. A ray‐tracing method and current gain calculation are used to evaluate the performance of the designed mirrors. The ray‐tracing result shows that the ideal resolution of quasi‐ellipsoidal mirrors with four‐segment conical approximation is 1.354 mm. As the source radius decreases from 20 mm, the neutron current with the designed focusing mirrors can be enhanced by a factor of 13 to over 100 compared with that without focusing mirrors in the same detected area. The effective collecting area is 186 cm2 when the source radius is the optimal 15 mm. An 83‐fold current gain can be obtained for cold neutrons. The proposed mirrors can reach 90.7 and 87.3% of the maximum current of the corresponding optimal mirror structure when the source radii are 10 and 20 mm, respectively. The results demonstrate that the proposed mirrors are adaptable for instruments with changeable sources. [ABSTRACT FROM AUTHOR]

The problem of dynamic diffraction of slow neutrons from a point source on the spatial lattice of a crystal with a weak deformation field is considered. The study is based on the asymptotic representation of the Green-Riemann function for a pair of Hamilton's equations of the hyperbolic type and describes the propagation of quasi-amplitudes of slow neutrons diffracted waves in a crystal lattice. The conditions for focusing one of the wave modes inside the crystal are considered. The main parameters of the focal spots inside of the lattice were investigated depending on the distance between the source of slow neutrons and the crystal. The behavior of focal spots from the parameter of the deformation field was also analyzed in detail. [ABSTRACT FROM AUTHOR]

In a recent paper [C. E. Bertrand et al., J. Chem. Phys. 145, 014502 (2016)], we have shown that the collective dynamics of methanol shows a fast relaxation process related to the standard density-fluctuation heat mode and a slow non-Fickian mode originating from the hydrogen bonded molecular associates. Here we report on the length scale dependence of this slow relaxation process. Using quasielastic neutron scattering and molecular dynamics simulations, we show that the dynamics of the slow process is affected by the structuring of the associates, which is accessible through polarized neutron diffraction experiments. Using a series of partially deuterated samples, the dynamics of the associates is investigated and is found to have a similar time scale to the lifetime of hydrogen bonding in the system. Both the structural relaxation and the dynamics of the associates are thermally activated by the breaking of hydrogen bonding. [ABSTRACT FROM AUTHOR]

A description and the performance of the very small angle neutron scattering diffractometer at the National Institute of Standards and Technology are presented. The measurement range of the instrument extends over three decades of momentum transfer q from 2 × 10−4 to 0.7 Å−1. The entire scattering angle range from 8 × 10−5 to π/6 rad (30°) can be measured simultaneously using three separate detector carriages on rails holding nine 2D detector arrays. Versatile choices of collimation options and neutron wavelength selection allow the q resolution and beam intensity to be optimized for the needs of the experiment. High q resolution is achieved using multiple converging‐beam collimation with circular pinholes combined with refractive lenses and prisms. Relaxed vertical resolution with much higher beam intensity can be achieved with narrow slit collimation and a broad wavelength range chosen by truncating the moderator source distribution below 4 Å with a Be crystalline filter and above 8 Å with a supermirror deflector. Polarized beam measurements with full polarization analysis are also provided by a high‐performance supermirror polarizer and spin flipper, capable of producing flipping ratios of over 100, along with a high‐efficiency 3He polarization analyzer. [ABSTRACT FROM AUTHOR]

• We show a new algorithm for propagating waves with Dirichlet boundary conditions. • It involves the use of Fast Fourier Fransforms and Green's functions. • Suitable for cases involving short wavelengths compared to waveguide dimensions. • Computational costs improved by two to three orders of magnitude. We present a new, efficient and robust method for computing scalar wave propagation for those cases in which Dirichlet boundary conditions play a key role. The algorithm is versatile and it allows to treat reflection, diffraction, waveguiding regime, scattering and free propagation. The analysis is based upon a representation for a slow neutron wavefunction in terms of the incoming wave and integrals, along the boundaries of an unbounded domain, involving a Green's function and certain auxiliary functions (warranting the Dirichlet boundary conditions). The analysis involves Fourier and Hilbert transforms defined only on the boundaries and enables to exploit the detailed advantages of Fast Fourier Transform (FFT) to perform simulations. Our algorithm proves to be highly effective both in terms in running time and memory load, compared to those based on Finite Differences Methods (FDM). Moreover, since the value of the field at each point may be calculated independently, this algorithm allows parallelization in a natural way. [ABSTRACT FROM AUTHOR]

A unique and important property of the neutron is that it possesses magnetic moment. This property is widely used for determination of magnetic structure of crystalline samples observing the magnetic components of the diffraction peaks. Investigations of diffraction patterns give information only about the averaged structure of a crystal but for discovering of local spin arrangement around a specific (e.g., impurity) nucleus remains still a challenging problem. Neutron holography is a useful tool to investigate the local structure around a specific nucleus embedded in a crystal lattice. The method has been successfully applied experimentally in several cases using non-magnetic short range interaction of the neutron and the nucleus. A mathematical model of the hologram using interaction between magnetic moment of the atom and the neutron spin for polarized neutron holography is provided. Validity of a polarized neutron holographic experiment is demonstrated by applying the proposed method on model systems.VC [ABSTRACT FROM AUTHOR]

The Monte Carlo ray-tracing simulation package McStas is verified by modeling two double axis neutron diffractometers, KARL and KANDI-II, located at the Israel Research reactors IRR-1 and IRR-2, respectively. The advantage of simulating these instruments is their simple design and small number of components. We focus on the simulation of a Soller slit collimator as well as Pyrolytic Graphite and Copper single crystal monochromators. The simulation is compared to neutron flux measurements, performed via activation analysis along the neutron beam as well as observed diffraction patterns from different powder samples. Calculated diffraction patterns are found to agree with observations to within 20%–50% in reflection peak width, while calculated attenuation of the neutron beam agrees to within 20% when the entire instrument is considered, and can show a discrepancy of up to 60% for individual components. Finally, a possible optimization of the neutron flux in the KARL diffractometer is presented. [ABSTRACT FROM AUTHOR]

The antiperovskite Mn3GaC undergoes an isostructural cubic--cubic first order transition from a low-temperature, large-cell-volume antiferromagnetic state to a high-temperature, small-cell-volume ferromagnetic state at around 160K. The transition can also be induced by applying a magnetic field. We study here the isothermal magnetic-field-evolution of the transition as ferromagnetism is stabilized at the expense of antiferromagnetism. We make use of the presence of the two distinct cell volumes of the two magnetic states as a probe to observe by neutron diffraction the evolution of the transition, as the external magnetic field carries the system from the antiferromagnetic to the ferromagnetic state. We show that the large-volume antiferromagnetic and the small-volume ferromagnetic states coexist in the temperature range of the transition. The ferromagnetic state is progressively stabilized as the field increases. [ABSTRACT FROM AUTHOR]

BiFeO3-PbTiO3 exhibits both ferroelectric and antiferromagnetic order, depending on the composition. Moderate hydrostatic pressures have been used at room temperature to transform the crystallographic phase from P4mm to R3c for the compositions 0.7BiFeO3-0.3PbTiO3 and 0.65BiFeO3-0.35PbTiO3, as determined using in-situ neutron diffraction. Using Rietveld refinements, the resultant data showed that, for both compositions, a transformation from para- to G-type antiferromagnetic order accompanied the structural transition. The transformation occurred over the range 0.4-0.77 and 0.67-0.88 GPa for 0.7BiFeO3-0.3PbTiO3 and 0.65BiFeO3-0.35PbTiO3, respectively; at intermediate pressures, a mixture of P4mm and R3c phases were evident. These pressures are far lower than required to induce a phase transition in either the BiFeO3 or PbTiO3 end members. The driving force for this pressure induced first order phase transition is a significant difference in volume between the two phases, P4mm > R3c of 4%-5%, at ambient pressure. Upon removal of the pressure, 0.65BiFeO3-0.35PbTiO3 returned to the paramagnetic tetragonal state, whereas in 0.7BiFeO3-0.3PbTiO3 antiferromagnetic ordering persisted, and the structural phase remained rhombohedral. Using conventional laboratory x-ray diffraction with a hot-stage, the phase readily reverted back to a tetragonal phase, at temperatures between 100 and 310 °C for 0.7BiFeO3-0.3PbTiO3, far lower than the ferroelectric Curie point for this composition of 632 °C. To our knowledge, the reported pressure induced para- to antiferromagnetic transition is unique in the literature. [ABSTRACT FROM AUTHOR]

We report changes in the metric symmetry of unpoled and electrically poled single crystals of 0.26Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.28PbTiO3, as revealed by neutron diffraction in conjunction with electrical measurements. The unpoled crystals show relaxor characteristics and an average rhombohedral symmetry that persists from ambient temperature up to the Curie temperature of ∼165 °C. Poling along a [111] direction enhances the rhombohedral distortion away from cubic metric symmetry but appears not to induce any monoclinic phases. By contrast, the poled [001]-oriented crystal has orthorhombic (or monoclinic MC) metric symmetry at 25 °C. An intermediate transition to a metrically tetragonal phase around 120 °C is confirmed for both poled crystals. [ABSTRACT FROM AUTHOR]

We present a summary description of the 8th annual international Design and Engineering of Neutron Instruments Meeting (DENIM) which was held in North Bethesda, MD, USA, September 17–19, 2019. DENIM VIII was organized by the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) in combination with the University of Maryland (UMD). DENIM specifically addresses the unique field of neutron instrument engineering, a subcategory of neutron scattering science. DENIM is organized by engineers for engineers who share openly about what works and what doesn't work in the life cycle design of an instrument used to analyze materials with neutrons. DENIM is held under the patronage of the International Society of Neutron Instrument Engineers which was formed in 2017. At DENIM VIII, there were 3 keynote talks, 29 additional presentations and 13 posters (presented to the plenary in a poster slam session). Attendees toured the unique labs at NIST including the NCNR. Four parallel knowledge sharing sessions helped attendees explore mutual challenges and solutions in the areas of Instrument Installation Survey and Alignment, Electrical Grounding, Choppers and Velocity Selectors, and 3D Printing. [ABSTRACT FROM AUTHOR]

In neutron optics, we analyse the propagation of slow (thermal) neutrons along a semi-infinite waveguide limited by a large repulsive potential (reminding the propagation of light along an optical fibre). We set an ideal case of a straight empty two-dimensional semi-infinite waveguide limited by an infinitely repulsive potential (Dirichlet conditions on its boundaries). The neutron wave function is given through an integral representation involving the incoming wave with energy E, Green's function and certain functions defined on the boundaries. The latter functions follow from the Dirichlet conditions, thereby proposing a new formalism in neutron optics. We develop various approximations (through Fourier and Hilbert transforms) and numerical computations. We get: (a) the expected extinction of the incoming wave for very large penetration into the waveguide, (b) the generation of propagation modes and their number for suitably large penetration, as E increases, (c) an estimate of the critical angle. [ABSTRACT FROM AUTHOR]

As continuously shaped super-mirrors are becoming available, the conceptual design of focusing guides should explore a wider range of possibilities to accomplish an efficient neutron beam extraction. Starting from a desired phase-space volume at the sample position and using an upstream ray-tracing approach, the acceptance diagram of any focusing guide can be calculated at the moderator position. To ensure high brilliance transfer and homogeneous coverage, the acceptance diagram should be fully included in the neutron source emission phase-space volume. Following this idea, the guide system can be scaled into dimensionless geometric figures that convey performance limits for a desired cross-section reduction. Moreover, if we impose a monotonic increase of the reflection angle with divergence angle at the sample position, the shape of the mirror is analytically determined. This approach was applied in the design of a focusing guide for SNAP instrument at SNS, at ORNL, USA. The results of McStas simulations are presented with different options included. Our approach facilitates finding an optimal solution for connecting multiple guide pieces to avoid excessive losses and ensure a homogeneous phase space coverage. [ABSTRACT FROM AUTHOR]

In the development of the European Spallation Source, the engineering phase of the Neutron Beam Extraction System is approaching its end. Currently, prototyping is ongoing to verify and increase the understanding of the manufacturing limitations in relation to the engineering aspects and beam extraction requirements from the instruments. After that the manufacturing of the suite of 16 neutron beam port inserts (NBPI) and light shutter systems (LSS) are phased into final detail design and manufacturing. The NBPIs have been developed as a close collaboration between ESS' instruments design coordinators and intricately integrate a set of copper optics within a controlled atmosphere within the target monolith pressure vessel. The NBPIs therefore includes not only a processed atmosphere but also enables fine alignment of the optics assemblies within it, but also includes a system for inserting it into a very precisely aligned and measured position. Outside the NBPIs, along the neutron beam paths, sits the Neutron Beam Windows and sequentially, the LSS which incorporates an optical bridge beam guide before the beam enters the bunker area and the individual instrument beam transports. ESS have chosen the concept of LSS, which generates demanding requirements for alignment of moving shutter parts. These system parts are placed in the bunker area and bunker basement, areas that are partly accessible during maintenance periods. [ABSTRACT FROM AUTHOR]

As continuously shaped super-mirrors are becoming available, the conceptual design of focusing guides should explore a wider range of possibilities to accomplish an efficient neutron beam extraction. Starting from a desired phase-space volume at the sample position and using an upstream ray-tracing approach, the acceptance diagram of any focusing guide can be calculated at the moderator position. To ensure high brilliance transfer and homogeneous coverage, the acceptance diagram should be fully included in the neutron source emission phase-space volume. Following this idea, the guide system can be scaled into dimensionless geometric figures that convey performance limits for a desired cross-section reduction. Moreover, if we impose a monotonic increase of the reflection angle with divergence angle at the sample position, the shape of the mirror is analytically determined. This approach was applied in the design of a focusing guide for SNAP instrument at SNS, at ORNL, USA. The results of McStas simulations are presented with different options included. Our approach facilitates finding an optimal solution for connecting multiple guide pieces to avoid excessive losses and ensure a homogeneous phase space coverage. [ABSTRACT FROM AUTHOR]

The high frequency part of the depolarized light scattering susceptibility has been measured for ortho-terphenyl (OTP) in a broad temperature and pressure range and analyzed using the mode-coupling theory (MCT). We found that the time-temperature-pressure superposition does not work for OTP in the frequency range of the susceptibility minimum and both a and b exponents of the MCT are temperature and pressure dependent. The pressure induced shift of the position of the minimum is much weaker than that of the α-peak resulting in dT[SUBc]/dP = 8.5 K/kbar while dT[SUBg]/dP = 26 K/kbar. Thus any universal scaling of the entire susceptibility including both the α-peak and the MCT minimum is not possible. These results are in contradiction to the previously reported conclusions obtained from the analysis of incoherent neutron scattering data [A. Tölle et al., Phys. Rev. Lett. 80, 2374 (1998)]. [ABSTRACT FROM AUTHOR]

The emergence of the uncertainty principle has celebrated its 90th anniversary recently. For this occasion, the latest experimental results of uncertainty relations quantified in terms of Shannon entropies are presented, concentrating only on outcomes in neutron optics. The focus is on the type of measurement uncertainties that describe the inability to obtain the respective individual results from joint measurement statistics. For this purpose, the neutron spin of two non-commuting directions is analyzed. Two sub-categories of measurement uncertainty relations are considered: noise–noise and noise–disturbance uncertainty relations. In the first case, it will be shown that the lowest boundary can be obtained and the uncertainty relations be saturated by implementing a simple positive operator-valued measure (POVM). For the second category, an analysis for projective measurements is made and error correction procedures are presented. [ABSTRACT FROM AUTHOR]

The problem of the interaction of ultracold neutrons with a neutron interference filter oscillating in space is investigated. In the problem, the evolution of the wave packet is considered by means of numerically solving the non-stationary Schrödinger equation by splitting the evolution operator. The filter oscillating in space acts as a quantum modulator of the ultracold neutron flux. The resulting spectra of the transmitted and reflected states are obtained depending on the motion parameters of the interferometer. [ABSTRACT FROM AUTHOR]

Placing a compound refractive lens (CRL) as an objective in a neutron beam generates new possibilities for 2D and 3D nondestructive mapping of the structure, strain and magnetic domains within extended objects. A condenser setup is introduced that allows correction for the lateral chromatic aberration. More generally, for full‐field microscopy the loss in performance caused by the chromatic aberration can be more than offset by introducing arrays of CRLs and exploiting the fact that the field of view can be much larger than the physical aperture of the CRL. Comments are made on the manufacture of such devices. The potential use is illustrated by comparisons between state‐of‐the‐art instrumentation and suggested approaches for bright‐field microscopy, small‐angle neutron scattering microscopy, grain mapping and mapping of stresses. Options are discussed for depth‐resolved imaging inspired by confocal light microscopy. Finally, experimental demonstrations are given of some of the basic properties of neutron full‐field imaging for a single CRL. [ABSTRACT FROM AUTHOR]

Spin-orbit coupling of light has come to the fore in nanooptics and plasmonics, and is a key ingredient of topological photonics and chiral quantum optics. We demonstrate a basic tool for incorporating analogous effects into neutron optics: the generation and detection of neutron beams with coupled spin and orbital angular momentum. The 3He neutron spin filters are used in conjunction with specifically oriented triangular coils to prepare neutron beams with lattices of spin-orbit correlations, as demonstrated by their spin-dependent intensity profiles. These correlations can be tailored to particular applications, such as neutron studies of topological materials. [ABSTRACT FROM AUTHOR]

Neutron current is crucial for neutron scattering measurements, especially for those at compact sources. Among various neutron optical devices, neutron-focusing mirrors have been drawing increasing attention due to their great potential in enhancing neutron current on sample for small-angle neutron scattering instruments. The state-of-the-art neutron-focusing mirrors, which can collect a large divergence of neutron beam, are required to be nestable and simultaneously be able to be coated with supermirrors. In this paper, we employ the nested conical optics to manufacture nested neutron-focusing mirrors with supermirror coatings. This technique enables such mirrors by assembling partial cylindrical glass segments into nested shells. A prototype system, containing two shell conical mirrors with m =2 Ni/Ti supermirror coatings, has been designed and manufactured. Ray-tracing simulations and neutron beam experiments have been carried out to evaluate its focusing performance and neutron reflectivity. The results show that neutron current collected by this prototype system is about 26 times higher than that by a pinhole design with the same Q min. Moreover, we discuss some possible further improvements on the fabrication process. [ABSTRACT FROM AUTHOR]

With the construction of the ESS, the European neutron user community is eagerly awaiting the commissioning of the brightest neutron source worldwide in 2021. Parallel to this, there is however the ongoing development of neutron science being undertaken at a dwindling number of neutron facilities worldwide. The Jülich Centre for Neutron Science has started a project to develop and design compact accelerator-driven high brilliance neutron sources as an efficient and cost effective alternative to the current low- and medium-flux reactor and spallation sources with the potential to offer science and industry access to neutrons. The project aims to deliver a high brilliance neutron source (HBS), consisting of a compact neutron production and moderator system which provides thermal and cold neutrons with high brilliance efficiently extracted in an optimized neutron transport system. By shaping the experiment holistically from the source to the detector, neutron experiments could be set-up for specific scientific requirements in a flexible and efficient way for the neutron user. [ABSTRACT FROM AUTHOR]

In this paper, some results of neutron diffraction properties of the dispersive double-crystal Si(111) + Si(311) and Si(111) + Si(400) monochromator settings containing two bent perfect crystals but with the second one – analyzer in the strongly asymmetric diffraction geometry, are presented. For the sake of possible applications, both double crystal settings were tested in the orientation of the second crystal for the output beam compression geometry. Powder diffraction test was carried out on a α -Fe(211) pin of the diameter of 2 mm. Contrary to the Si(111) + Si(400) setting, an excellent resolution represented by full width at half maximum in the (Δd/d)-scale was obtained for the Si(111) + Si(311) double crystal monochromator in the parallel as well as in the antiparallel diffraction geometry. [ABSTRACT FROM AUTHOR]

Abstract The Multipurpose Physics neutron diffractometer (MP) will be built at the China Spallation Neutron Source (CSNS) in the coming years. It is a time of flight diffractometer dedicated to the study of complex crystalline materials through the total scattering or pair distribution function (PDF) technique. The MP diffractometer will be able to determine the PDF from the atomic to the nanometer scale. We present a validation of the main physical parameters of the MP diffractometer through Monte Carlo simulation. In particular the moderator choice, guide system and placement of the chopper system is investigated. The best momentum transfer resolution δ Q/Q is reached in backscattering and is expected to be in the order of 0.2 %, the neutron flux at the sample is of the order of 107 n/s/cm2 and the momentum transfer range in the order of 0.08–100 Å −1. [ABSTRACT FROM AUTHOR]

The crystal structures of α‐F2 and β‐F2 have been reinvestigated using neutron powder diffraction. For the low‐temperature phase α‐F2, which is stable below circa 45.6 K, the monoclinic space group C2/c with lattice parameters a=5.4780(12), b=3.2701(7), c=7.2651(17) Å, β=102.088(18)°, V=127.26(5) Å3, mS8, Z=4 at 10 K can now be confirmed. The structure model was significantly improved, allowed for the anisotropic refinement of the F atom, and an F−F bond length of 1.404(12) Å was obtained, which is in excellent agreement with spectroscopic data and high‐level quantum chemical predictions. The high‐temperature phase β‐F2, stable between circa 45.6 K and the melting point of 53.53 K, crystallizes in the cubic primitive space group Pm3‾n with the lattice parameter a=6.5314(15) Å, V=278.62(11) Å3, cP16, Z=8, at 48 K. β‐F2 is isotypic to γ‐O2 and δ‐N2. The centres of gravity of the F2 molecules are arranged like the atoms in the Cr3Si structure type. Fluorine: The crystal structures of α‐F2 and β‐F2 have been reinvestigated using neutron powder diffraction. For α‐F2, the structure model was significantly improved, allowed for the anisotropic refinement of the F atom. Data are in excellent agreement with spectroscopic investigations and high‐level quantum chemical predictions. [ABSTRACT FROM AUTHOR]

Examines the neutron reflectivity of a multilayer system with interface roughness on the basis of the neutron optical method. Experiments conducted; Measurement of reflectivity and transmittivity; Discussion.

Abstract Nanocomposites enable us to tune parameters that are crucial for use of such materials for neutron-optics applications. By careful choice of properties such as species (isotope) and concentration of contained nanoparticles, diffractive optical elements for long-wavelength neutrons are feasible. Nanocomposites for neutron optics have so far been tested successfully in protonated form, containing high amounts of 1 H atoms, which exhibits rather strong neutron absorption and incoherent scattering. At a future stage of development, chemicals containing 1H could be replaced by components containing more favorable isotopes, such as 2 H or 19F. In this note, we present results of Monte-Carlo simulations of the transmissivity of various nanocomposite materials for thermal and very-cold neutron spectra. Our simulation results for deuterated and fluorinated nanocomposite materials predict the losses due to absorption and scattering to be as low as 2%, as well as the broadening of the beam cross section to be negligible. [ABSTRACT FROM AUTHOR]

Abstract Structure of binary Fe-19Ga and ternary Fe-19Ga-Tb alloys at room temperature are investigated by TEM and high-resolution neutron diffraction (ND). In contrast with as cast or water quenched samples with A2 structure, the D0 3 ordering was detected in slowly cooled or annealed samples by ND. According to TEM, the D0 3 ordering takes place in the form of ordered clusters with the size of about 5 nm embedded into an A2 matrix. Disordering of the D0 3 clusters at heating and ordering at cooling were investigated by three in situ techniques: ND, vibrating sample magnetometry (VSM), and internal friction (IF). Temperatures of ordering-disordering were estimated by VSM and IF to be close to 500 °C. The effect of Fe-Ga alloys doping with Tb is also analyzed. Graphical abstract Image 1 Highlights • Fe-19Ga alloys structure is examined at room temperature and up to 800 °C. • Different cooling regimes lead to formation of A2 or D0 3 structure. • D0 3 structure stability is examined at heating and cooling by several in situ methods. [ABSTRACT FROM AUTHOR]

Abstract The mechanical behavior of cold-rolled Mg AZ31B is studied during in-plane multiaxial loading and tension-tension strain path changes performed on cruciform samples using in situ neutron diffraction and EBSD. The results are compared with uniaxial tension loading of dogbone-shaped samples measured with in situ neutron diffraction and acoustic emission. The activity of slip and twinning mechanisms and the active twin variants are discussed for the different strain paths. It is shown that initial strains of 4–5% cause a strengthened yield stress during reload for strain path change angles of 90 and 135°. The strengthening is primarily due to dislocation accumulation during the initial load impeding dislocation motion during the reload. The twinning observed during the prestrain activates complex multivariant secondary twinning which may also contribute to the strengthening in the reload. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Purification of C2H4 from an C2H4/C2H6 mixture, one of the most important while challenging industrial separation processes, is mainly through energy‐intensive cryogenic distillation. Now a family of gallate‐based metal–organic framework (MOF) materials is presented, M‐gallate (M=Ni, Mg, Co), featuring 3D interconnected zigzag channels, the aperture sizes of which (3.47–3.69 Å) are ideally suitable for molecular sieving of ethylene (3.28×4.18×4.84 Å3) and ethane (3.81×4.08×4.82 Å3) through molecular cross‐section size differentiation. Co‐gallate shows an unprecedented IAST selectivity of 52 for C2H4 over C2H6 with a C2H4 uptake of 3.37 mmol g−1 at 298 K and 1 bar, outperforming the state‐of‐the‐art MOF material NOTT‐300. Direct breakthrough experiments with equimolar C2H4/C2H6 mixtures confirmed that M‐gallate is highly selective for ethylene. The adsorption structure and mechanism of ethylene in the M‐gallate was further studied through neutron diffraction experiments. [ABSTRACT FROM AUTHOR]

Abstract The crystal and magnetic structure of brownmillerite Ca 2 Fe 2-x Al x O 5 ; x = 0.8 has been refined against the powder neutron diffraction data collected as a function of temperature from 3 K to 350 K. Ca 2 Fe 2-x Al x O 5 is a G-type antiferromagnet with Ibm 2 symmetry, the magnetic ion Fe occupies both tetrahedral and octahedral sites and both the sites are antiferromagnetically coupled individually. In this report, the mechanism of spin reorientation transition shown by these compounds is elucidated. The moment direction is found to be directed preferably along the crystallographic c -axis at low temperatures along with a small fraction of domains that are aligned along the a -axis. As the temperature is increased the domain with a -axis aligned moment inflates at the expense of domains with the moment directed along c -axis. However, at all temperatures both types of domains are found to be coexisting. The results suggest phase coexistence of the two magnetic structures with temperature dependent dynamics. [ABSTRACT FROM AUTHOR]

The investigation of crystal and magnetic structures of BaFe 12 - x Me x O 19 ( Me = In 3 + and Ga 3 + ; x = 0.1–1.2) solid solutions has been carried out by time-of-flight neutron diffraction method. It was determined the influence of diamagnetic In and Ga ions to unit cell volume of partially substituted barium ferrites. The electric field-induced polarization was observed in the BaFe 11.9 Me 0.1 O 19 (Me = In and Ga) solid solutions at room temperature. The refinement of crystal structure of barium ferrites has been carried out in frameworks of two possible space group: centrosymmetric P 6 3 / mmc (No. 194) and non- centrosymmetric P 6 3 mc (No. 186) that allowed to reveal reasons of appearance of nonzero dipole electric moment. For description of magnetic structure of BaFe 12 - x Me x O 19 (Me = In and Ga; x = 0.1–1.2) solid solutions was used the Gorter’s model where magnetic moments of iron ions are oriented along the hexagonal axis that is the axis of easy magnetization. [ABSTRACT FROM AUTHOR]

The replacement of the H16-IN5 guide has been decided in the frame of the ILL Endurance program. This guide is made of heteroclite sections and the upgrade aims at improving the performances with a modern homogeneous ballistic guide. Several constraints applied to the project: (i) the instrument will remain at the same location, (ii) considering (i), in terms of gain relative to cost, it was judged more reasonable to keep the same chopper system, (iii) many technical elements under control of the nuclear safety authorities cannot be changed within the lifetime of the project. We present the results of the McStas optimization of the replacing guide performed under these constraints. [ABSTRACT FROM AUTHOR]

Overview of the future guide systems at the ILL. [ABSTRACT FROM AUTHOR]

As the world's leading centre for neutron science, the ILL provides scientists with a very high flux of neutrons. The transport of neutrons to the different instruments is continually being adapted to the latest technologies in order to maximise the useful neutron flux available. Dedicated neutron guides can now be created with a geometry and wavelength spectrum that are optimised for individual instruments and this paper gives an overview on the recent achievements as well as some insight on guides projects foreseen for the ILL future. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of the oxidation of thin titanium films and their use in neutron spin optics. Kinetics of Ti nanofilm oxidation (at T = 200 ° C) was found to be described by the logarithmic law. The asymptotic law of the oxide layer growth and the long-term stability of the Ti/TiO2 bilayer demonstrate the possibility of using the Ti nanofilms in neutron spin optics. It is experimentally proven that a protective Ti layer reliably prevents the oxidation of the functional magnetic layer of the mirror spin-flipper. [ABSTRACT FROM AUTHOR]

Fundamental optical concepts are utilized across all fields of scientific instrumentation. In the case of beam-like systems in neutron scattering instrumentation (low-divergence trajectories taken over long distances), quantities describing a system can be scaled into dimensionless figures of merit that convey performance characteristics and geometric limits. Furthermore, this first-principles approach facilitates a straight forward means by which to tailor an optical system to a defined source-sample configuration, as well as further inform guide surface shapes and reflectivity requirements. These principles will be presented and applied incorporated to examples showing their relevance to practical applications and future instrumentation. [ABSTRACT FROM AUTHOR]

The idea of treating the trinucleon systems as elementary entities in the elementary particle model (EPM) as an Effective Field Theory has been a success in explaining the weak charge-changing processes in nuclei. The EPM results are found to be as good as those obtained from nuclear microscopic models using two-and three-body forces. We extend this concept to investigate the validity of the elemental nature of A = 3 nuclei through studies of nuclear structure of neutron-rich nuclei. By treating neutron-rich nuclei as primarily made up of tritons as its building blocks, we extract one- and two-triton separation energies of these nuclei. Calculations have been performed here within relativistic mean field (RMF) models with latest interactions. Clear evidence arises of a new shell structure with well-defined predictions of new magic nuclei. These unique predictions have been consolidated by standard one- and two-neutron separation energy calculations. The binding energy per nucleon plots of these nuclei also confirm these predictions. We make unambiguous prediction of six magic nuclei: 8 2 4 O 1 6 , 2 0 6 0 Ca 4 0 , 3 5 1 0 5 Br 7 0 , 4 1 1 2 3 Nb 8 2 , 6 3 1 8 9 Eu 1 2 6 and 9 2 2 7 6 U 1 8 4 . [ABSTRACT FROM AUTHOR]

Possible options for modernization of the neutron beam forming system of the DN-6 diffractometer for the study of crystal and magnetic structures of microsamples at high pressures are being considered. It was demonstrated that for samples with the cross-section not exceeding 5 × 5 mm 2 the most efficient option would be the use of an elliptical neutron guide. It allows to deliver neutrons for large distances from the source to samples with minimal losses using, as a rule, just one neutron reflection per dimension i.e. one at a side and one at top or bottom. For the present moment due to technical difficulties of such option realization, the simplified solution was proposed. At the end of the curved neutron guide it is planned to install a vertical plane focusing 7-meter-long parabolic section. Such a modernization will increase the neutron flux at the sample by a factor 1.5–3.5 and reduce respectively the typical measurement times. [ABSTRACT FROM AUTHOR]

The calculation of neutron reflectivity from raw time‐of‐flight data including instrumental corrections and an improved resolution calculation is presented. The theoretical calculations are compared with experimental data measured on the vertical sample plane reflectometer D17 and the horizontal sample plane reflectometer FIGARO at the Institut Laue–Langevin (ILL), Grenoble, France. This article comprises the mathematical body of the time‐of‐flight reflectivity data‐reduction software COSMOS which is used on D17 and FIGARO. [ABSTRACT FROM AUTHOR]

A new production process allows a direct bonding of HOPG crystals on Si wafers. This new method facilitates the production of analyzer crystals with support structure without the use of additional, background inducing fixation material, e.g. glue, wax and screws. This new method is especially interesting for the upcoming generation of CAMEA-type multiplexing spectrometers. These instruments allow for a drastic performance increase due to the increased angular coverage and multiple energy analysis. Exploiting the transparency of multiple HOPG for cold neutrons, a consecutive arrangement of HOPG analyzer crystals per Q-channel can be achieved. This implies that neutrons travel through up to 10 arrays of analyzer crystals before reaching the analyzer corresponding to their energy. Hence, a careful choice of the fixation method for the analyzer crystals in regards to transparency and background is necessary. Here, we present first results on the diffraction and mechanical performance of direct bonded analyzer crystals. [ABSTRACT FROM AUTHOR]

Neutron reflectivity is a powerful technique for characterizing interfaces in many areas of science. The traditional method of time of flight for measuring the wavelength of neutrons in a white beam is extremely wasteful, as the vast majority of neutrons must be absorbed in the choppers in order to produce a pulsed beam. A prism operates continuously, with a transmission up to two orders of magnitude higher than choppers. The wavelength‐dependent deflection of the beam by the prism, coupled with a high spatial resolution detector, results in excellent wavelength resolution. The theory of how the resolution is considerably enhanced by curving the surface of the prism is described in detail for a real experimental arrangement. It is demonstrated how this can be used for faster neutron reflectometry, including the merging of different angles and subtraction of background. The technique shows considerable promise for neutron reflectivity, opening up new areas of science particularly in the realms of kinetics and small samples. [ABSTRACT FROM AUTHOR]

We discuss the potential for neutron spectrometers at novel accelerator driven compact neutron sources. Such a High Brilliance Source (HBS) relies on low energy nuclear reactions, which enable cryogenic moderators in very close proximity to the target and neutron optics at comparably short distances from the moderator compared to existing sources. While the first effect aims at increasing the phase space density of a moderator, the second allows the extraction of a large phase space volume, which is typically requested for spectrometer applications. We find that competitive spectrometers can be realized if (a) the neutron production rate can be synchronized with the experiment repetition rate and (b) the emission characteristics of the moderator can be matched to the phase space requirements of the experiment. MCNP simulations for protons or deuterons on a Beryllium target with a suitable target/moderator design yield a source brightness, from which we calculate the sample fluxes by phase space considerations for different types of spectrometers. These match closely the figures of todays spectrometers at medium flux sources. Hence we conclude that compact neutron sources might be a viable option for next generation neutron sources. [ABSTRACT FROM AUTHOR]

Simple and fast analytic method to find optimal combinations of sizes of neutron moderator and optical system entrance, allowing for the full sample illumination with minimum to none background, is developed. In the case of employing low-dimensional para-hydrogen moderators with enhanced neutron beam brilliance, the method allows to determine the minimum size of moderator, which provides the highest sample flux while keeping the sample fully illuminated. This method can be used during the design of new neutron sources, upgrades of neutron optical systems and moderator replacements. [ABSTRACT FROM AUTHOR]