Long-wavelength Neutrons Research Articles

MENUS—Materials engineering by neutron scattering

Materials engineering by neutron scattering (MENUS) at the second target station will be a transformational high-flux, versatile, multiscale materials engineering diffraction beamline with unprecedented new capabilities for the study of complex materials and structures. It will support both fundamental and applied materials research in a broad range of fields. MENUS will combine unprecedented long-wavelength neutron flux and unique detector coverage to enable real-time studies of complex structural and functional materials under external stimuli. The incorporated small angle neutron scattering and transmission/imaging capabilities will extend its sensitivity to larger length scales and higher spatial resolution. Multimodal MENUS will provide crystallographic and microstructure data to the materials science and engineering community to understand lattice strain/phase transition/microstructure/texture evolution in three orthogonal directions in complex material systems under combined extreme applied conditions. The capabilities of MENUS will open new scientific opportunities and meet the research needs for science challenges to enable studies of a range of phenomena and answer the key questions in material design/exploration, advanced material processing, transformative manufacturing, and material operations of national impacts in our daily life.

Investigating the magnetic ground state of the skyrmion host material Cu2OSeO3 using long-wavelength neutron diffraction

We present long-wavelength neutron diffraction data measured on both single crystal and polycrystalline samples of the skyrmion host material Cu2OSeO3. We observe magnetic satellites around the (01¯1) diffraction peak not accessible to other techniques, and distinguish helical from conical spin textures in reciprocal space. Our measurements show that not only the field-polarised phase but also the helical ground state are made up of ferrimagnetic clusters instead of individual spins. These clusters are distorted Cu tetrahedra, where the spin on one Cu ion is anti-aligned with the spin on the three other Cu ions.

Monte-Carlo simulation of neutron transmission through nanocomposite materials for neutron-optics applications

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 1H 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 2H 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.

The effect of aluminium on twinning in binary alpha-titanium

The deformation mechanisms of binary Ti–Al model alloys (0–13.1 at.% Aluminium) have been investigated with respect to the twinning activity using in-situ loading in combination with neutron diffraction as well as detailed post mortem electron backscatter diffraction analysis. A consistent starting grain size and texture was generated for all alloys promoting tensile twinning during compression testing. Long-wavelength neutron diffraction and selected area diffraction transmission electron microscopy analysis were carried out to detect evidence of Aluminium ordering and Ti3Al formation.It was found that raising the Aluminium content in Titanium does first slightly enhance twinning, with {101¯2}<101¯1> tensile twinning being by far the dominant type, while the critical residual intergranular strains for twin initiation decreases. This suggests that either the lowering of stacking fault energy by Aluminium or its solute solution strengthening effect are important factors. At around 7 at.% Aluminium a turning point in twinning activity was noticed and a further increase in Aluminium did result in a dramatic loss of twinning activity particularly when the material had been exposed to an additional low temperature age. The dramatic decrease of twinning activity is strongly correlated with increasing evidence of short range ordering and also early signs of Ti3Al-formation in case of the highest Aluminium content. In addition, electron backscatter diffraction analysis revealed that the formation of Aluminium ordered zones do severely hinder growth of twin boundaries.

Current status of advanced pelletized cold moderators development for IBR-2M research reactor

The world’s first advanced pelletized cold neutron moderator is prepared to be put into operation at the IBR-2M pulsed research reactor. It provides long-wavelength neutrons to the most of neutron spectrometers at the beams of the IBR-2M reactor. Aromatic hydrocarbons are used as a material for cold moderators. It is a very attractive material because of its high radiation resistance, good moderating properties, incombustibility, etc. It is shown that the idea of beads transport by a helium flow at cryogenic temperatures is successful. The recent progress and plans for moderator development at the IBR-2M reactor as well as the experimental results of beads transport are discussed in the paper.

The 40 m general purpose small-angle neutron scattering instrument at Oak Ridge National Laboratory

A series of upgrades have been undertaken at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, including the installation of a supercritical hydrogen moderator (T≃ 20 K), which has boosted the flux of long-wavelength neutrons by over two orders of magnitude. In order to take advantage of the new capabilities, a 40 m-long small-angle neutron scattering (SANS) instrument has been constructed, which utilizes a mechanical velocity selector, pinhole collimation and a high-count-rate (&gt;105 Hz) large-area (1 m2) two-dimensional position-sensitive detector. The incident wavelength (λ), resolution (Δλ/λ), incident collimation and sample-to-detector distance are independently variable under computer control. The detector can be moved up to 45 cm off-axis to increase the overallQrange [&lt;0.001 &lt;Q= (4π/λ)sinθ &lt; 1 Å−1, where 2θ is the angle of scatter]. The design and characteristics of this instrument are described, along with examples of scattering data to illustrate the performance.

Experimental verification of the simulated performance of a compact supermirror focusing device

Large gains in neutron flux on small samples are possible for long-wavelength neutrons using appropriately designed short pieces of m = 3 supermirrors in the incident beam close to the sample. These devices are particularly attractive for existing instruments on spallation neutron sources as they provide a simple method for increasing flux whilst leaving the majority of the incident beam infrastructure unchanged. This paper will describe recent results from a measurement of the performance of a two-dimensional supermirror focusing device on the SURF instrument at ISIS. Particular attention was paid to the effect of misalignment in order to obtain a quantitative measure of the precision to which such components would have to be remotely positioned in the more enclosed environment of instruments such as the SXD single crystal diffractometer at ISIS. The experimental flux gain and beam divergence are also compared with results from Monte Carlo simulations of the SURF instrument with and without the focusing device.

Roton Excitation Spectrum in Liquid Helium II

We derive a one-particle quantum equation for roton excitations by considering rotons as bound states of helium atoms. Our approach is based on a self-similar solution of the nonlinear Schr\odinger equation with a self-consistent confining potential in a roton cluster surrounded by the condensate. The symmetric vibrational excitation of the roton determines the gap in the energy spectrum of the elementary excitations in liquid He II. Analysis of the scattering process of long-wavelength neutrons from the liquid on the basis of our theory leads directly to Landau's roton spectrum of excitations with an effective roton mass and energy spectrum gap that are in quantitative agreement with the experimental data.

Neutrons for the future

The neutron community has expanded enormously since nuclear physicists made the first measurements of neutron cross-sections in the 1940s. Crystallographers started to exploit the potential of the new technique in the 1950s and were soon joined by condensed-matter physicists. The advent of “cold” neutron sources, which provided a rich flux of long-wavelength neutrons, attracted chemists and later biologists to neutron scattering. And in the last decade or so engineers, materials and earth scientists have joined the club, all attracted by the unique possibilities that neutron scattering is offering to their fields.

Optical potential and dispersion law for long-wavelength neutrons

The method of multiple-wave scattering theory is applied to the calculation of reflection and refraction of neutrons at the interface of an ideal crystalline medium. The expression for the optical potential for the interaction of slow neutrons with the medium is considered. The relation between wave vectors in the media and in the vacuum is discussed. The anomalies declared in previous work are shown to be absent.

Modern optics of long-wavelength neutrons

This paper is dedicated to the memory of Academician Il'ya Mikhailovich Frank (1908–1990). The papers of I.M.Frank for the period 1972–1974 concerning the optics of ultracold neutrons (UCN) are briefly reviewed and compared with later results obtained in this field. The basic stages of the development of a neutron microscope based on UCN are briefly described. The possibility of using neutron-optical methods for fundamental investigations with long-wavelength neutrons is discussed.

Possible investigation of liquid-vapor phase transition with a realistic interface using long-wavelength neutrons

It is shown that the coexistence curve of a classical fluid ( 4He as an example) with realistic interface profiles can be mapped with high precision, minimal gravity distortion, and to the immediate vicinity of the critical point by employing the interference of long wavelength neutrons from a thin film of the fluid.

Cold Neutron Research Facility Begins Operating at NIST

Materials scientists, condensed matter physicists, analytical chemists and biologists are only part of a large and growing community of researchers who need access to subthermal, or “cold,” neutrons and the various instruments that use these very-lowenergy particles. For the past two decades, many US researchers have had to travel to Western Europe for that access, but now, with the opening of the new, $30-million Cold Neutron Research Facility at the National Institute of Standards and Technology in Gaithersburg, Maryland, intense beams of long-wavelength neutrons are available closer to home.

Sovremennaya optika dlinnovolnovykh neitronov

Sovremennaya optika dlinnovolnovykh neitronov

Possible application of graphite–SbCl5intercalation compounds as long-wavelength neutron monochromators

Neutron diffraction measurements on highly oriented pyrolytic graphite intercalated with SbCl5 have been carried out and indicate that these intercalation compounds have practical application as long-wavelength neutron monochromators. This is due, in part, to their large d spacings and, in part, to their long-range c-axis stacking fidelity and chemical stability. The stage 2 compound is particularly suitable because it has intense first-order scattering accompanied by very weak second-order scattering. These intensity considerations are not as favorable for the stage 4 compound but applications at longer wavelengths are possible. At a scattering angle of 60° (2θ) neutrons of wavelengths 12.8 and 19.5 Å can be obtained from the stage 2 and stage 4 compounds, respectively. Structure-factor calculations for the 001 peaks are presented and are found to be in reasonable agreement with the diffraction data.

Imaging and focusing of neutrons by a zone plate

The use of refractive lenses for long-wavelength neutrons,although possible1, is severely limited by the fact that the refractive index differs only very slightly from unity (forexample, n − 1 = 2.3 × 10−4for quartz at λ = 20 A). However, the fact thatonly a relatively thin layer of material is needed to produce an optical path difference of half a wavelength (for example, 2.4 µm of Cu at λ = 20 A) led us to propose2 previously that neutrons could be focused by diffraction froma phase grating of variable spacing; this is , in fact, a type of zone plate. Zone plates, first described by Soret3, have been used satisfactorily over a large part of the electromagneticspectrum4–6. We now report the successful focusing and imaging of a slow neutron beam by means of a Fresnel zone plate8.

The small-angle neutron scattering facility at the SAFARI-1 reactor

A long-wavelength neutron scattering facility at the SAFARI-1 reactor is described. Neutrons of wavelength between 5 and 15 Å can be selected. Features of the facility are the use of microwave guides as neutron conductors, flexible guide-pipe configuration and automatic sequential sample changing. Examples are given of measurements on radiation-induced voids in copper, aluminium, Al-0.4%Si and Al-0.1%In after neutron irradiation and magnetic scattering in US and in 80US-10UC-10UC2.

Diffuse neutron scattering in niobium containing interstitial oxygen impurities

The elastic diffuse scattering of long-wavelength neutrons ( lambda =4.95 AA) by niobium-oxygen BCC solid-solution alloys NbO0.026 and NbO0.036 has been studied in the (001) reciprocal plane for 0.2<4 pi sin theta / lambda <2.25 AA-1. Broad intensity peaks were found around the (100), (1/200) and (1/21/20) reciprocal lattice points. There was no small-angle scattering. The diffuse scattering due to the distortion of the lattice by random oxygens in octahedral or tetrahedral sites was calculated in the (100) and (110) directions and agreed with the experimental data only in the long-wavelength limit. The observed diffuse intensity peaks were then attributed to short-range ordering of interstitial oxygen. The authors' conclusion is that the clusters inferred by Gibala and Wert (1966) from internal friction data are not random, but correlated up to distances of the order of 20 AA, at least in (001) planes.

Ferromagnetism in iron-chromium alloys. II. Neutron scattering studies

Diffuse neutron scattering measurements have been made on ferromagnetic iron-chromium alloys containing 15-, 30-, 50-, and 73-at.% Cr with the long-wavelength neutron spectrometer at Harwell. The results have been analyzed, within the framework of the Marshall model, to determine both the average moments at the iron and chromium sites and the disturbances in the individual moments arising from fluctuations in the near-neighbor environent. The average moment per iron atom rises to a small maximum around 15-at.% Cr and then decreases as the chromium concentration increases. The average chromium moment is negative and becomes smaller in magnitude as the chromium concentration increases. The sum of the disturbances at the iron and chromium sites changes sign as a function of concentration. The range of the disturbance appears to be smaller in chromium-rich than in iron-rich alloys.

Long-wavelength neutron scattering studies of the decomposition of Al–Zn alloys

Determination of whether a spinodal mechanism or a nucleation and growth mechanism giving rise to Guinier–Preston zones is responsible for the initial stages of the decomposition sequence of low-zinc-concentration aluminium alloys at room temperature.