Table of contents

We describe here recent inelastic neutron scattering experiments on the heavy fermion compound URu₂Si₂ realized in order to clarify the nature of the hidden order (HO) phase which occurs below T₀ = 17.5 K at ambient pressure. The choice was to measure at a given pressure P where the system will go, by lowering the temperature, successively from paramagnetic (PM) to HO and then to antiferromagnetic phase (AF). Furthermore, in order to verify the selection of the pressure, a macroscopic detection of the phase transitions was also achieved in situ via its thermal expansion response detected by a strain gauge glued on the crystal. Just above P_x = 0.5 GPa, where the ground state switches from HO to AF, the Q0 = (1,0,0) excitation disappears while the excitation at the incommensurate wavevector Q1 = (1.4, 0, 0) remains. Thus, the Q0 = (1, 0, 0) excitation is intrinsic only in the HO phase. This result is reinforced by studies where now pressure and magnetic field H can be used as tuning variable. Above Px, the AF phase at low temperature is destroyed by a magnetic field larger than H_AF (collapse of the AF Q₀ = (1, 0,0) Bragg reflection). The field reentrance of the HO phase is demonstrated by the reappearance of its characteristic Q₀ = (1, 0, 0) excitation. The recovery of a PM phase will only be achieved far above H_AF at H_M ≈ 35 T. To determine the P-H-T phase diagram of URu₂Si₂, macroscopic measurements of the thermal expansion were realized with a strain gauge. The reentrant magnetic field increases strongly with pressure. Finally, to investigate the interplay between superconductivity (SC) and spin dynamics, new inelastic neutron scattering experiments are reported down to 0.4 K, far below the superconducting critical temperature T_SC ≈ 1.3 K as measured on our crystal by diamagnetic shielding.

We performed inelastic neutron scattering (INS) in order to re-investigate the crystal-field ground state and the level splitting in UO₂. Previous INS studies on UO₂ by Amoretti et al. [Physical Review B 15, 1989, 1856] uncovered four excitations at low temperatures in the 150-180 meV range. Considering the dipole-allowed transitions, only three of these transitions could be explained by the published crystal-field model. Our INS results on a different UO₂ sample revealed that the unaccounted peak at about 180 meV is a spurious one, and thus not intrinsic to UO₂. In good agreement with Amoretti's results, we corroborated that the ground-state of UO₂ is the Γ₅ triplet, and we computed that the fourth-and six-order crystal field parameters are V₄ = -116 meV and V₆ = 26 meV, respectively. We also studied the INS response of the non-magnetic U₀₄Th₀₆O₂. The splitting for this thorium-doped compound is similar to the one of UO₂, which orders antiferromagnetically at low temperatures. Therefore, we can conclude that magnetic interactions only weakly perturb the energy level splitting, which is dominated by strong crystal fields.

The high flux and low background of the new backscattering spectrometer at the SNS combine to produce an excellent signal to noise ratio, allowing us to investigate a low lying weak excitation never seen before in the spin ice, Ho₂Ti₂O₇. This non-dispersive excitation has been observed at E = 26.3 μeV below 100 K but is resolution limited only below ∼ 65 K. It is indifferent to magnetic fields below μ₀H = 4.5 T, at 1.6 K. These characteristics help us to identify the excitation as due to the nuclear spin system.

The series R₂PdSi₃ (R = heavy rare earth) has been found to exhibit rich magnetic phase diagrams with a large variety of magnetic states. This complex magnetic behavior results from the interplay between RKKY interaction, magneto-crystalline anisotropy based on crystalline-electric field (CEF) effects and geometric frustration due to the AlB₂ derived hexagonal crystal structure. Within the series the Er₂PdSi₃ compound has been found to exhibit in zero field a simple CEF excitation spectrum with just one strong transition at 3.5 meV from the ground state to the first excited state. Neutron spectroscopy in magnetic fields up to 12 T has been performed on the cold-triple axis spectrometer PANDA at FRM II. In this study two transitions within the 3.5 meV excitation could be resolved showing a linear dependency in applied magnetic fields with an almost identical slope of μ_Bg_L for fields above 2 T. The results can be explained in a picture of two slightly different sets of CEF parameters for two inequivalent Er³⁺ sites due the crystallographic superstructure observed in all single crystals of type R₂PdSi₃.

LiCoPO⁴ (T_N ≈ 21.8 K) & LiMnPO₄ (T_N ≈ 34 K) are antiferromagnetic insulators exhibiting large magnetoelectric effects. We performed inelastic neutron scattering (INS) experiments to investigate the spin dynamics of these systems and analyzed the measured magnetic spectra by linear spin-wave theory, taking into account intra- and inter-plane nearest, next nearest neighbor magnetic exchange interactions and single ion anisotropy. The INS results indicate that the single ion anisotropy in LiCoPO₄ is comparable to the nearest-neighbor magnetic exchange interaction rendering Ising-type behavior of LiCoPO₄. Neutron diffraction studies of LiMnPO₄ in applied magnetic fields reveal a spin-flop transition at ∼ 3.5 Tesla with characteristics of a second order phase transition.

The neutron scattering from hydrogen in polythene has been measured with the direct time-of flight spectrometer, MARI, at the ISIS facility of the Rutherford Appleton Laboratory with incident neutron energies between 0.5 eV and 600 eV. The results of experiments using the spectrometer, VESUVIO, have given intensities from hydrogen containing materials that were about 60% of the intensity expected from hydrogen. Since VESUVIO is the only instrument in the world that routinely operates with incident neutron energies in the eV range we have chosen to measure the scattering from hydrogen at high incident neutron energies with a different type of instrument. The MARI, direct time-of-flight, instrument was chosen for the experiment and we have studied the scattering for several different incident neutron energies. We have learnt how to subtract the gamma ray background, how to calibrate the incident energy and how to convert the spectra to an energy plot . The intensity of the hydrogen scattering was independent of the scattering angle for scattering angles from about 5 degrees up to 70 degrees for at least 3 different incident neutron energies between 20 eV and 100 eV. When the data was put on an absolute scale, by measuring the scattering from 5 metal foils with known thicknesses under the same conditions we found that the absolute intensity of the scattering from the hydrogen was in agreement with that expected to an accuracy of ± 5.0% over a wide range of wave-vector transfers between 1 and 250 Å⁻¹. These measurements show that it is possible to measure the neutron scattering with incident neutron energies up to at least 100 eV with a direct geometry time-of-flight spectrometer and that the results are in agreement with conventional scattering theory.

The cubic Prussian Blue (PB) analog, Zn₃ [Fe(CN)₆]₂, has been studied by X-ray powder diffraction and inelastic neutron scattering (INS). X-ray data collected at 300 and 84 K revealed negative thermal expansion (NTE) behaviour for this material. The NTE coefficient was found to be −31.1 × 10⁻⁶ K⁻¹. The neutron vibrational spectrum for Zn₃[Fe(CN)₆]₂.xH₂O, was studied in detail. The INS spectrum showed well-defined, well-separated bands corresponding to the stretching of and deformation modes of the Fe and Zn octahedra, all below 800 cm⁻¹.

Extensive inelastic neutron scattering measurements of phonons on a single crystal of CaFe₂As₂ allowed us to establish a fairly complete picture of phonon dispersions in the main symmetry directions. The phonon spectra were also calculated by density functional theory (DFT) in the local density approximation (LDA). There are serious discrepancies between calculations done for the optimized structure and experiment, because the optimised structure is not the ambient pressure structure but is very close to the "collapsed" structure reached at p = 3.5 kbar. However, if the experimental crystal structure is used the calculation gives correct frequencies of most phonons. The most important new result is that linewidths/frequencies of certain modes are larger/softer than predicted by DFT-LDA. We also observed strong temperature dependence of some phonons near the structural phase transition near 172 K. This behavior may indicate anomalously strong electron phonon coupling and/or anharmonicity, which may be important to the mechanism of superconductivity.

A transition to a superconducting state was recently observed in the binary alloy of FeSe_1-xTe_x system where TC rises with increasing x. The substitution of the larger Te for Se ion results in no additional charges but increases the internal chemical pressure. Earlier studies suggested that the crystal structure maintains the tetragonal P4/nmm symmetry with the substitution of Te where the average bond angle, α, decreases considerably from ∼ 104° in FeSe to 100.5° in the mixed phase of FeSe_0.5Te_0.5. With the use of pulsed neutron power diffraction and the Rietveld analysis, the crystal structure refinement for FeSe_0.5Te_0.5 yielded very large thermal factors in the superconducting phase indicative of the presence of structural distortions that may be significant in understanding the electronic and magnetic properties of this system.

We report the results of single-crystal neutron diffraction studies of the superconductor BaNi₂As₂. The experiments were performed on a tiny crystal of mass 0.8 mg at several temperatures between 20 and 200 K using the Single Crystal Diffractometer, SCD, at the Los Alamos Neutron Science Center. Above 130 K, BaNi₂As₂ crystallizes in the tetragonal ThCr₂Si₂ structure. Our neutron diffraction data corroborate a first-order structural transition around 130 K with a relatively large hysteresis of about 10 K, in agreement with observations from bulk studies. The anisotropic thermal displacement coefficients are enhanced along c-axis approaching the transition, and a splitting is observed for in-plane type reflections below the transition, which is evidence for a change in crystal structure.

We report measurements of the evolution of the diffuse scattering in a single crystal PbMg1/3Nb2/3O3 as a function of hydrostatic pressure. Upon applying pressure the diffuse scattering intensity decreases and is suppressed at about 3 GPa, while no change in the line shape is observed. Correlations between Pb displacements, diffuse scattering and relaxor properties are discussed.

We have used neutron powder diffraction to make a comprehensive study of the crystal structure in Pr₂Fe₁₇ nanocrystalline compounds. These nanostructured materials have been obtained by high-energy ball milling from an arc-melted bulk polycrystalline alloy. The Th₂Zn₁₇-type rhombohedral crystal structure of the starting bulk alloy is maintained after milling for 10 and 20 hours. The studied alloys are ferromagnetic below T_C = 286±1 K (bulk) and T_C ≈ 300±20 K (milled). These materials exhibit strong magneto-volume anomalies below T_C, such as a negative coefficient of thermal expansion (α_V ≈ -30 × 10⁻⁶ K⁻¹).

A neutron diffraction structure study has been performed on newly synthesized Ge₂₀As₂₀Se₅₀Te₁₀ and Ge₂₇As₁₃Se₅₀Te₁₀ chalcogenide glasses. Oscillations in the structure factor, S(Q) have been measured with good sign-to-noise up to 35 Å⁻¹. The reverse Monte Carlo simulation was used to model the 3-dimensional atomic configuration. The partial atomic correlation functions and structure factors have been revealed. Several first and second neighbour distances, and coordination numbers have been calculated. We have established that several first neighbour atomic distances are overlapping at two characteristic distances, namely the Ge-Ge, Ge-Se and As-Se are centred at 2.42 Å, while the Ge-Te, As-Te and Se-Te are centred at 2.60 Å.

Magnetic and local structures in an antiperovskite system, Mn₃Cu_1-xGe_xN, with a giant negative thermal expansion have been studied by neutron powder diffraction measurement. We discuss (1) an importance of an averaged cubic crystal structure and a ΓG^5g antiferromagnetic spin structure for the large magneto-volume effect (MVE) in this itinerant electron system, (2) an unique role of a local lattice distortion well described by the low temperature tetragonal structure of Mn₃GeN for the broadening of MVE.

The magnetic structure of the perovskite cobaltite La_0.82Ba_0.18CoO₃ was investigated using powder neutron diffraction. Although macroscopically this composition is thought to be in the spin-glass phase from bulk magnetic measurements, the presence of Bragg-like magnetic features in the neutron diffractograms suggests otherwise. At 4 K, two long-range magnetic orders are observed with two propagation wave vectors, k₁ = (0,0,0) and k₂ = (0,-0.5,0.5), corresponding to ferromagnetic and antiferromagnetic orders, respectively. However, above 100 K, the k₂ component almost disappears, while k₁ persists.

NaFeGe₂O₆ is a one of the representatives of the pyroxene family with the general formula Me¹⁺Me³⁺Si(Ge)2O6 (Me¹⁺- monovalent metal cation, Me³⁺-3-d transition metal cation), which regained strong interest in spintronics as a new class of multiferroic materials and in solid-state physics as a quasi-low-dimensional insulating system. The sodium iron germanate NaFeGe₂O₆ powder was synthesized at 800°, 900° C for 4 days from the stoichiometric mixture of Na₂CO₃, Fe₂O₃, GeO₂ by solid state reaction after several cycles of regrinding. Using neutron powder diffraction the magnetic order below T_N ≈ 13 K was found and the magnetic structure has been determined. It is incommensurate and consists of antiferromagnetically coupled Fe³⁺ pairs with helical modulation within the a-c plane of the crystal lattice.

Due to the interplay between RKKY exchange interaction, crystalline-electric field (CEF) effects and geometric frustration due to the AlB₂-derived hexagonal crystal structure, the study of R₂PdSi₃ (R = rare earth) has been found to be a challenging field in rare earth magnetism. In this contribution we present the results of neutron diffraction experiments on a Ho₂PdSi₃ single crystal in the magnetically ordered state at T = 1.6 K. The compound orders antiferromagnetically in the basal plane with the propagation vector τ = (1/7-δ, 2δ, 0) where δ ∼ 0.01 r.l.u. In magnetic fields applied along the (10) magnetic hard axis, the structure persists up to the highest measured field of 5 T. The dependence of the intensities as a function of field suggests that the τ structure is a single-k multi-domain structure.

A NdCr₂Si₂C polycrystal has been prepared and characterized by heat-capacity and magnetization, X-ray and neutron powder diffraction measurements. Ferromagnetism below TC = 21 K with Nd magnetic moments aligned parallel to the c-axis has been confirmed. We also studied the electronic structure of NdCr₂Si₂C by first-principles calculations, which predict the ordered magnetic moment both on the Nd and Cr sites. The magnetization and neutron diffraction data, however, do not allow resolving the question of existence of the Cr moment unambiguously.

A ternary intermetallic compound CeIr₃Si₂ shows successive magnetic transitions at T_N1=4.1 K and T_N2=3.3 K. At T < T_N2 it shows three-step metamagnetic transitions below H=1.43 T. In this non-diluted compound a long-time variation of magnetic structure has been detected by means of time-resolved neutron scattering measurements. When a sample is rapidly cooled below T_N2, the magnetic Bragg peaks corresponding to the intermediate temperature phase (T_N2< T < T_N1) are observed. The amplitude of these Bragg peaks gradually decreases with time. On the other hand, another group of Bragg peaks corresponding to the low temperature phase (T < T_N2) gradually grow with time. The characteristic time for these variations follows the Arrhenius law with an activation energy E_a/k_B =4 K.

We have determined the magnetic structure of Er₃Cu₄Si₄ by high-resolution neutron powder diffraction down to 0.34 K. The magnetic ordering temperatures of the Er(2d) and Er(4e) sublattices are 14 K and 3.3 K, respectively. The Er(2d) order is commensurate down to 0.34 K, with a propagation vector [0 1/2 0] and a moment of 8.7(2) μ_B at 0.34 K. The Er(4e) order is initially short-range and incommensurate, with a propagation vector [0 0.876(5) 0] and a refined moment of only 4.4(2) μ_B 1.5 K. Below about 1.4 K, the Er(4e) order starts to lock-in to a commensurate cell described by the propagation vector [1/3 1/2 1/2] with the moments aligned in the crystal bc-plane, canted about 4° away from the b-axis. The lock-in is complete by 0.8 K and the Er(4e) moment is 8.8(2) μ_B at 0.34 K.

For the study of antiferromagnetism in thin-film materials, neutron diffraction is a particularly important tool, especially since magnetometry experiments are often complicated by the substrate's strong diamagnetic or paramagnetic contribution. However, the substrate, by necessity, has a lattice parameter that is very similar to that of the film, and in most cases is over 1000 times more massive than the film. Therefore, even weak structural distortions in the substrate crystal may complicate the analysis of magnetic scattering from the film. Here we show that in contrast to most other perovskite substrates (including SrTiO₃, LaAlO₃, etc.), KTaO3 provides a uniquely appropriate substrate platform for magnetic diffraction experiments on epitaxial oxide films.

The RNi_1-xCu_xAl pseudoternaries belong to group of RTX intermetallic compounds crystallizing in the hexagonal ZrNiAl type of structure. In the critical region of the substitution parameter x ∼ 0.8 there was found a loss of a long-range magnetic order at the lowest studied temperatures for series with R = Tb, Dy, Er. As an explanation for this effect a competition of different ordering mechanisms for either RNiAl or RCuAl compounds was proposed. Nevertheless, the magnetization curves of the ErNi_0.2Cu_0.8Al compound (within the critical concentration region) showed behaviour close to the parent ErCuAl, which was confirmed as a ferromagnet. Neutron diffraction on ErNi_0.2Cu_0.8Al compound with applied magnetic field signifies appearing of the ferromagnetic order at the lowest applied magnetic field of 0.1 T. The magnitude of the ordered magnetic moment increases with increasing magnetic field in agreement with the magnetization curve, confirming tendency to ferromagnetic ordering or short-range magnetic order of ferromagnetic character in this critical region.

Results of neutron diffraction measurements on TbNiSn in magnetic fields up to 6T are reported. This material shows successive phase transitions at T₁ = 7.6 K, T₂ = 6.0 K, T₃ = 2.0 K and T_N = 18.5 K in zero field, and a giant magnetoresistance effect (GMR) near four successive metamagnetic transitions at low temperatures. Propagation vectors and main signatures of the magnetic phases appearing at elevated fields applied along the b axis at low temperatures are determined. We find large hysteresis at several phase boundaries. In some cases a co-existence of magnetic structures is detected.

The magnetic and structural properties of the low-dimensional (2D) Ising magnet KEr(MoO₄)₂ are investigated in a temperature region from 70 mK to 8 K in zero field and in external magnetic fields up to 6 T. At 1.8 K, an additional scattering contribution appears at forbidden nuclear reflection positions when ramping an external magnetic field along the c*-axis, showing appreciable hysteresis. This is in agreement with already observed peculiarities in the EPR spectra, microwave absorption spectra and the differential magnetic susceptibility. The low temperature magnetic contribution to the scattering recorded at temperature of 70 mK is confronted with a zero field non-collinear four-lattice magnetic structure magnetic model suggested in the literature.

The susceptibility of four MAX phases (Ti₂AlC, Cr₂AlC, Ti₃AlC₂, and Ti₃SiC₂) to high-temperature thermal dissociation in vacuum has been investigated using in-situ neutron diffraction. In high vacuum, these phases decomposed above 1400°C through the sublimation of M and A elements, forming a surface coating of MC. The apparent activation energies for the decomposition of sintered Ti₃SiC₂, Ti₃AlC₂, and Ti₂AlC were determined to be 179.3, -71.9, and 85.7 kJ mol⁻¹, respectively. The spontaneous release of Ti₂AlC and TiC from de-intercalation during decomposition of Ti₃AlC₂ resulted in a negative activation energy.

The magnetic phase diagrams of hexagonal R₂PdSi₃ compounds have been found to feature an apparent similar phase when the field is applied along the respective magnetic easy axes. To elucidate this, neutron diffraction on single crystalline Tb₂PdSi₃ and Ho₂PdSi₃ in magnetic fields was performed. These two compounds have different magnetic structures in zero field. In Tb₂PdSi₃ the propagation vector is parallel to the hexagonal axis while in Ho₂PdSi₃ the propagation is in the basal plane. In both compounds the magnetic moment direction is perpendicular to the propagation vector. The application of a magnetic field along the respective easy axes destroys the zero field magnetic structure and leads to a ferrimagnetic phase with magnetic intensity on the same positions for both compounds. These findings and their connections to the crystallographic (super-)structure are presented and discussed.

Au_xZn_1-x alloys undergo a shape memory martensitic transformation whose temperature and nature (continuous or discontinuous) is strongly composition dependent. Neutron diffraction experiments were performed on single crystals of x=50 and 52 to explore the structural changes occurring at the transition temperature. A transverse modulation with wavevector q₀=(1/3,1/3,0) develops below the transition temperature, with no observable change in lattice parameter. However, the Bragg peak width shows a broadening suggesting an unresolved rhombohedral distortion similar to what has been observed in NiTi-Fe alloys.

Single crystals of BiRe₂O₆ of typical volume 0.03 mm³ were grown by chemical vapor transport and characterized using room-temperature single-crystal neutron diffraction in monoclinic C2/c symmetry with cell parameters a = 16.1178(11), b = 4.9235(3), c = 5.5278(3) Å and β = 92.475(5) ° (R_all = 11.39 wR_all = 7.97). The structure contains ordered layers of corner sharing units of Re₂O₁₀ with Re-Re distances of 2.519(1) Å. The unit cell is doubled along c in comparison to previous studies based on X-ray diffraction data where the layer stacking was described as disorderd.

Partial substitution of manganese for titanium in bismuth titanate is a potential method to introduce ferromagnetic properties to ferroelectric bismuth titanate. We have established that manganese-substituted bismuth titanate forms only at low manganese contents. As the manganese content is increased, secondary phases form. A combination of neutron and synchrotron X-ray powder diffraction has been used to determine the structure of manganese-substituted bismuth titanates with chemical composition Bi₄Mn_xTi_{3_x}O₁₂ (0 ≤ x ≤1 at 0.05 steps). Measurements between 4 K and 1073 K have been used to examine the phase transitions that they undergo. It was found the substitution of manganese into bismuth titanate increases the phase transition temperature to tetragonal by about 100 °C. Neutron diffraction and bulk magnetic susceptibility measurements demonstrate the absence of long-range magnetic cation ordering in selected examples.

A crystallization phase diagram defining the meta-stable region of bovine β-lactoglobulin A (β-Lg) was firstly determined by a dialysis method. We have succeeded in growing a large single crystal of β-Lg by selecting a crystal grown in this "meta-stable region" method described in the present paper. The quality of protein crystals was characterized quantitatively via rapid X-ray data collections, followed by the use of Wilson plots to analyze their resulting average B-factors.

Since 2004, Ibaraki prefecture has constructed the TOF neutron biological diffractometer (iBIX) at J-PARC for industrial use. Since the end of 2008, Ibaraki University has operated iBIX in order to support the experiment of users and to improve the instruments. The diffractometer is designed to measure samples with their cell edges up to around 150Å. In the beginning of December in 2008, the basic optics, the support system of detectors and the three detectors were completed for the diffraction experiments. We have tried to measure the TOF diffraction data of several proteins and organic compounds in order to estimate the efficiency and characteristics of the diffcactometer. The TOF diffraction data of Ribonuclease A can be measured under the following conditions, beam power: 20kW, pulse repetition: 25Hz, range of wavelength: 0.5∼4Å, exposure time: 18.7 hours. About one hundred Bragg reflections could be observed clearly on all detectors. The reflection of 1.58Å in minimum d-spacing which I_obs/γ(I_obs) > 7 was observed. This result implies that the efficiency of the iBIX will become 50∼100 times higher than that of the present high performance diffracatometer BIX-3 in JAEA after 1MW operation of J-PARC.

Achromobacter protease I (API, E.C. 3.4.21.50) is one of the serine proteases produced by Achromobacter lyticus M497-1. API is distinct from the other tripsin type protease in its lysine specificity. The neutron structure analysis of catalytic triad with Trp169 and His210 was presented. His57 was double protonated and formed hydrogen bonds to Ser194O^γ and Asp113O^δ1, O^δ2.

Trypsin is one of serine proteases. BPTI (Bovine Pancreatic Trypsin Inhibitor) is a protein inhibitor, which binds trypsin tightly and inhibits cleavage of peptide bonds. X-ray structure determination of trypsin-BPTI complex could make clear the overview of the active site. However, information of hydrogen atoms related to catalytic mechanism has not been satisfied. In this study, the trypsin-BPTI complex structure has been determined by neutron diffraction data at 2.0 Å resolution. Deuterium atoms of catalytic triad, hydration structures in the binding pocket of trypsin and hydrogen bonds were observed. We would like to discuss details of hydrogen bonds in the interface between trypsin and BPTI and the adjacent water molecules including hydrogen atoms involved in the enzymatic reaction.

We report on a small angle neutron scattering (SANS) study of a temperature driven first order phase transition in a 25wt% solution of the surfactant AOT (Sodium Di-2-ethylhexyl Sulfosuccinate) in 1.5wt% heavy brine between an isotropic L₃ "sponge" state at 27°C and a stacked lamellar L_α monophase 55°C. The prominent scattering features of these phases are correlation peaks due to the mean passage size of the L₃ sponge and the L_α stacking separation. This ratio of the monophase peak positions Q_α/Q₃≈1.3, is consistent with previous observations in this and similar systems. In the present study we tracked this system through the intermediate L₃ +L_α biphasic miscibility gap. There the initial appearance of the L_α peak at 33.25°C was at a scattering vector some 23% higher than the final high temperature monophase value. During coexistence both L₃ and L_α phase peak positions decreased linearly with increasing temperature maintaining a roughly constant ratio Q_α/Q₃ ∼1.6-1.7. Two phase fits to the scattering data and application of scaling law predictions allow us to obtain local L₃ phase volume fractions in the biphasic region and make preliminary determinations of the structural accomodations necessitated by phase coexistence in this system's miscibility gap.

From dibenzoyl cystine, a low molecular weight gelator, we have prepared needle shaped crystals at relatively high concentrations. For the first time SESANS measurements are performed on objects with this geometry. From the measurements the average diameter can be seen directly. From a more careful analysis the width distribution is determined. The gel phase itself prepared at lower concentrations did not show any signal, in contrast to what one observes with conventional SANS. This shows the complementarity of SESANS and SANS.

We have investigated the diffusion coefficient of nano-meter-sized domains on a vesicle composed of saturated phospholipids, unsaturated phospholipids and cholesterols by means of neutron spin echo spectroscopy. The obtained diffusion coefficient was examined from a viewpoint of the hydrodynamic model of Brownian objects in a fluid membrane.

We have studied how local anesthetics influence the structural and dynamical properties of model bio-membranes. The measurements of small-angle neutron scattering have been performed on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) unilamellar vesicles with different concentrations of lidocaine in D₂O to determine the bilayer thickness as a function of the lidocaine concentration. The neutron-spin echo spectroscopy (NSE) has been used to study the influence of lidocaine on the bending elasticity of DMPC bilayers in fluid crystal phase (L_α) and the ripple gel (P_β') phase.

Cholesterol is an essential component of mammalian cells, and is required for building and maintaining cell membranes, regulating their fluidity, and possibly acting as an antioxidant. Cholesterol has also been implicated in cell signaling processes, where it has been suggested that it triggers the formation of lipid rafts in the plasma membrane. Aside from cholesterol's physiological roles, what is also becoming clear is its poor affinity for lipids with unsaturated fatty acids as opposed to saturated lipids, such as sphingomyelin with which it forms rafts. We previously reported the location of cholesterol in membranes with varying degrees of acyl chain unsaturation as determined by neutron diffraction studies (Harroun et al 2006 Biochemistry45, 1227; Harroun et al 2008 Biochemistry47, 7090). In bilayers composed of phosphatidylcholine (PC) molecules with a saturated acyl chain at the sn-1 position or a monounsaturated acyl chain at both sn-1 and sn-2 positions, cholesterol was found in its much-accepted "upright" position. However, in dipolyunsaturated 1,2-diarachidonyl phosphatidylcholine (20:4-20:4PC) membranes the molecule was found sequestered in the center of the bilayers. In further experiments, mixing l-palmitoyl-2-oleoyl phosphatidylcholine (16:0-18:1 PC) with 20:4-20:4PC resulted in cholesterol reverting to its upright orientation at approximately 40 mol% 16:0-18:1 PC. Interestingly, the same effect was achieved with only 5 mol% 1,2-dimyristoyl phosphatidylchoile (14:0-14:0PC).

It is generally accepted that neutron diffraction from model membrane systems is an effective biophysical technique for determining membrane structure. Here we describe an example of how deuterium labelling can elucidate the location of specific membrane soluble molecules, including a brief discussion of the technique itself. We show that deuterium labelled α-tocopherol sits upright in the bilayer, as might be expected, but at very different locations within the bilayer, depending on the degree of lipid chain unsaturation.

We investigated the ternary Cu-Li-Mg system, in particular the CuLi_xMg_2-x (x = 0.08) for hydrogen storage. Instead of crystallizing in an orthorhombic phase, as CuMg2, this phase presents a hexagonal structure very similar to that of NiMg₂ and NiMg₂H_0.3. In this work we will discuss the structure of CuLi_xMg_2-x by the analysis of the neutron scattering data and first principles calculations. The first results for a hydride (deuteride) phase will also mentioned since preliminary studies at LANSCE showed that CuLi_xMg_2-x might absorb approximately 5.3 to 6 wt% of H at an equilibrium pressure of approximately 27 bar at 200 ^oC. If these results are confirmed in future work, this will mean that, not only CuLi_xMg_2-x absorbs a considerable amount of hydrogen (close to DOE's expectations for hydrogen storage materials), but also will probably release it at a temperature in the range of 50 to 150 ^oC, where applications are easier to develop. Hence it should be possible to use this alloy with fuel cells or in batteries. Another important observation is that cycling has a strong effect on the structure of the hydride.

The properties of spinach light harvesting complex II (LHC II), stabilized in the detergents Triton X-100 (TX100) and n-Octyl-β-D-Glucoside (BOG), were investigated by small-angle neutron scattering (SANS). The LHC II-BOG scattering curve overlaid well with the theoretical scattering curve generated from the crystal structure of LHC II indicating that the protein preparation was in its native functional state. On the other hand, the simulated LHC II curve deviated significantly from the LHC II-TX100 experimental data. Analysis by circular dichroism spectroscopy supported the SANS analysis and showed that LHC II-TX100 is inactivated. This investigation has implications for extracting and stabilizing photosynthetic membrane proteins for the development of biohybrid photoconversion devices.

Membrane proteins (MPs), which play vital roles in trans-membrane trafficking and signalling between cells and their external environment, comprise a major fraction of the expressed proteomes of many organisms. MP production for biophysical characterization requires detergents for extracting MPs from their native membrane and to solubilize the MP in solution for purification and study. In a proper detergent solution, the detergent-associated MPs retain their native fold and oligomerization state, key requirements for biophysical characterization and crystallization. SANS with contrast variation was performed to characterize BR in complex with OG to better understand the MP-detergent complex. Contrast variation makes it possible to not only probe the conformation of the entire structure but also investigate the conformation of the polypeptide chain within the BR-OG complex. The BR-OG SANS contrast variation series is not consistent with a compact structure, such as a trimeric BR complex surrounded by a belt of detergent. The data strongly suggest that the protein is partially unfolded through its association with the detergent micelles.

We have studied the structural properties of lipid bilayers made up of monounsaturated phosphatidylcholines (i.e. diCn:1PC, where n=14, 16, 18, 20, 22 and 24). High-resolution x-ray scattering data were analyzed in conjunction with contrast varied neutron scattering data, using the recently developed technique by Kučerka et al. [Biophys. J. 95, 2356 (2008)]. Analyses of the data show that with increasing n lipid bilayers do not thicken in a linear fashion, as is often assumed, but quadratically, and that lipid area assumes a maximum value for n∼18 bilayers. More importantly, compared to previous data our results strongly suggest that lipid areas are smaller by about 10%. This observation highlights the need to revisit lipid areas as they are extensively used in molecular dynamics simulations and for calibrating their force fields.

To perform neutron residual stress measurements it is often necessary to cut samples to a manageable size. The effects of cutting a girth welded pipe were investigated with analytical methods and finite element analysis. The effect of cutting on measured stresses was calculated. A simplified method of modelling residual stresses in welds, "chill modelling", is introduced.

In ring slitting a cut is made in the axial direction and the deformation is maeesured. The change in elastic stress can be calculated and added to neutron diffraction measurements made on a cut ring to calculate the original stresses. Residual stress measurements were performed to validate the ring slitting correction using ANSTO's residual stress diffractometer Kowari.

The branch analysed in this paper was not post weld heat treated, resulting in significant residual stresses. Assessment codes assume these to be at, or close to, yield. An integrity assessment of a welded branch connection was carried out using these high assumed residual stresses.

The weld then had residual stresses determined by neutron diffraction, performed using ANSTO's residual stress diffractometer, Kowari. The maximum measured residual stress (290 MPa or 60% of yield) was much lower than the yield value assumed by assessment codes. Reanalysing with the actual residual stresses almost doubled the critical crack size, increasing the safety of the connection.

Materials showing a large magnetic field induced strain can potentially substitute giant magnetostrictive materials as well as piezoelectrical ceramics in actuating devices. However the magnetic shape memory alloys face several problems for an industrial application. Besides the well known brittleness the temperature-range is still limited due to the structural and magnetic phase transition around 75°C. By alloying one of the most common systems Ni-Mn-Ga with 4.8 at% and 6 at% Cobalt the Martensite temperature was increased up to 422K and the Curie temperature up to 432K. Neutron diffraction experiments were performed on these Ni-Mn-Ga-Co single crystalline samples at room temperature, which show the existence of two different non-modulated martensitic structures. Dependent on the composition, a tetragonal and an orthorhombic structure in single crystalline samples were verified. Furthermore intermartenstic phase transitions above room temperature were determined in several samples alloyed with 6 at% cobalt. A temperature dependent measurement of the structure of Ni_44.6Mn_29.1Ga_20.1Co_6.2 showed an orthorhombic phase from room temperature up to 379K changing to a tetragonal intermartensitic phase before reaching the austenitic phase above 389K.

A neutron diffraction study on 6 Middle Bronze Age axes, cast from tin bronze or from arsenical copper, has been carried out using the ENGIN-X beamline at ISIS. The gauge volumes dimensions were 4x4x10mm³; data were collected along the lengths of the objects in their central parts, as well as on the blades, in order to establish the spatial phase contents. Average phase fractions were determined by Rietveld analysis. The main phases identified were solid solutions, corrosion phases and metallic Pb inclusions. We have observed distributions of lattice constants of the solid solutions Cu-Sn, and Cu-As inside each gauge volume in the central parts of the axes due to segregation, or liquation effects. However, the Cu-Sn variations were significantly less pronounced in comparison with typical inhomogeneity effects in as cast objects. The results indicate that the studied Middle Bronze Age axes were probably treated at high temperatures for homogenization necessary for generating sufficient hardness, especially on the blades.

The sintering of metal injection moulded stainless steel was investigated using in situ neutron diffraction with different sintering temperatures, from 1270°C up to 1390°C, with sintering profiles that were based on those used in industry. The production of an unwanted high temperature phase, δ-ferrite, was observed during sintering and is seen to be retained in the final product after sintering. Ferrite production during sintering acts to speed up the sintering process by forming in the grain pores but is unwanted in the final product as it is a soft and malleable phase. The ferrite that was formed at high temperature was observed to not completely disappear during cooling as a result of the coexistence of dual high temperature phases delta-ferrite and gamma-austenite during the high temperature soak. This suggests the segregation of the alloying elements between the two phase which changes the composition of the phase grains and allows the ferrite to exist during cooling, resulting in the unwanted phase in the final product.

There is a new generation of lasers available for materials processing. The new lasers include fibre and disc laser are characterized by very high beam quality at very high power levels providing extremely high energy density. In general laser welding is selected over other welding processes because of the minimisation of the heat input, residual stresses and distortion, for this reason they are increasingly popular over a wide range of industries. The narrowness of the welds makes it challenging to resolve the details of the residual stresses produced by the welding process. Residual strain/stress measurements of two specimens produced using the fibre laser were performed on Engin-X. Across the weld and through thickness distributions are reported in this paper.

Welding repairs are increasingly a structural integrity concern for aging pressure vessel and piping components. It has been demonstrated that the residual stress distribution near repair welds can be drastically different from that of the original weld. Residual stresses have a significant effect on the lifetime performance of a weld, and a reduction of these stresses is normally desirable. The aim of this paper is to investigate residual stresses in various weld repair arrangements using the non-destructive neutron diffraction technique. This research is focused on characterization of the residual stress distribution: (i) in the original weld; (ii) in a shallow toe weld repair; and (iii) after conventional post-weld heat treatment. The focus of the measurements is on the values of the subsurface strain/stress variations across the weld.

Residual strains in air plasma sprayed (APS) and high velocity oxy-fuel (HVOF) alumina (Al₂O₃) coatings were investigated by means of neutron diffraction technique. Results of this investigation conclude that through thickness residual strain in the APS coating was mainly tensile whereas the HVOF coating had both compressive and tensile residual strain. Further analysis of Vickers indentation fracture behaviour using acoustic emission (AE) technique concluded that the nature and magnitude of these residual strain fields had a direct effect on the fracture response of two coatings during the indentation process.

Oxide dispersion strengthened (ODS) reduced activation ferritic/martensitic steels are being developed for structural applications in future fusion reactors since they would allow consistently increasing the operation temperature The 9%CrWVTa Eurofer-97 steel has been selected as a base material strengthened by Y₂O₃ contents of 0.3 and 0.5 wt% and produced in a powdermetallurgical route by mechanical alloying and hot isostatic pressing (HIP). The mechanical properties are strongly correlated with Y₂O₃ particle average size and spatial distribution, therefore small-angle neutron scattering (SANS) is quite useful to investigate how these evolve in the course of the production steps. Solid polycrystalline samples as well as mechanically alloyed powders have been investigated after thermal treatments thus simulating the HIP conditions. The obtained SANS results show that annealing at high temperature results in a redistribution of scattering centres sizes, which might be attributed to the growth of small Yttria particles and possibly of larger carbides.

The China Advanced Research Reactor (CARR) and the China Spallation Neutron Source (CSNS), like other big national facilities for basic research in China, are viewed as vehicles for engaging in international R&D efforts, furthering the nation's technological advancement, and facing arduous challenges such as energy and materials needs. In 2009, CARR – a 60MW steady-state reactor in Beijing – is expected to reach criticality while the CSNS – an 120 kW pulsed source in Dongguan – is to begin construction. In spite of the differing schedule, the road leading to full operation of the sources and productive utilization of the neutron instruments will be a long one. From the outset both projects benefit a great deal through interactions with the worldwide neutron communities. An even more trenchant task is to build a domestic user base, presumably from China's numerous universities and research laboratories, to imbue new scientific ideas into using and exploiting of the neutron methodology. Arguably, a smaller neutron facility yet apt at flexibility and optimization for education and academic R&D is needed to bridge 'big' facilities and 'small' sciences. Here, we introduce the plan of a compact pulsed neutron source (driven by a 13MeV-proton accelerator system with a Be target and room-temperature and cryogenic moderators), to be built in about 3 years as a part of a Hadron Application Research Center at Tsinghua University. We discuss the mission of these neutron sources, the complementarity therein, and their synergetic relation with the academia and other facilities, and possible cooperation with international counterparts.

After the Spallation Neutron Source (SNS) construction project was completed in June, 2006, development of plans to construct a second target station (STS) at SNS began. These plans have evolved to the establishment of a reference concept for a STS and associated neutron beam instruments, and the evaluation of the expected performance for this station, all of which have been documented in a White Paper. Based on this White Paper, the Department of Energy has approved development of a detailed conceptual design leading to a construction project for the STS. The STS reference design is based on pulse stealing from the 60 Hz SNS accelerator system, with one pulse of every three going to the STS and the other two going to the first target station. The STS would operate in long-proton-pulse mode with no pulse compression in the accumulator ring, and would be optimized for production of intense beams of cold neutrons. The reference concept for the STS and the estimated performance for this concept will be discussed

We have constructed an instrument, CryoEDM, to measure the neutron electric dipole moment to a precision of 10⁻²⁸e cm at the Institut Laue-Langevin. The main characteristic is that it is operating entirely in a cryogenic environment, at temperatures of 0.7 K within superfluid helium. Ultracold neutrons are produced in a superthermal source and stored within the superfluid in a storage cell which is held in a magnetic and electric field. NMR measurements are carried out to look for any shifts in the neutron Larmor precession frequency associated with the electric field and the neutrons are detected in-situ in the superfluid. Low temperature SQUID magnetometry is used to monitor the magnetic field. We report on the current status of the project that is now being commissioned and give an outlook on the future exploitation of the instrument.

The basis of the Double-Crystal Diffractometer (DCD), used for ultra-small angle neutron scattering (USANS), is that the reflectivity function is very near 1.0 for |y| < 1, where y = (θ - θ_B)/ δΘ_D, falls off rapidly for |y| >1, eventually decreasing as y ⁻². In the Bonse-Hart multi-bounce crystal the reflectivity function R(y) transforms into R^m(y) and in the wings, for large |y|, theoretically decreases as y^−2m after m consecutive Bragg reflections inside the channel-cut crystal. Here θ and θB are respectively the diffraction angle and the Bragg angle (for given wavelength) and δΘ_D is the width of the Darwin plateau. However, the experimental reflectivity R^m_exp(y) obtained for m = 3 exceeds the theoretical prediction by over two orders of magnitude in the range of the far wings, which creates limitations for USANS studies of weakly scattering objects.

We used the pulsed-source neutron time-of-flight (TOF) technique to study this discrepancy in more detail. Two identical Si(111) crystals, a slab-shaped single-bounce and a channel-cut triple-bounce, were measured at the nominal Bragg angle θB = 24.4o in the TOF powder diffractometer GPPD at IPNS, in the range 0.2 < λ < 4.0 Å of the first seven Bragg reflections from Si(111) family. Cadmium shielding protected the detectors from view of the first-bounce crystal. The experimental data obtained from the single-bounce crystal shows thermal diffuse (phonon) scattering (TDS) filling the region between the Bragg reflections, and exhibiting the symmetry of the reciprocal lattice. With appropriate shielding installed, the triple-bounce Bragg reflections, in contrast, are TDS-free in the range 0.6 < λ < 3.0 Å; however, the intensity of TDS grows in the range λ < 0.5 Å, reaching the level of TDS registered for the single-bounce reflections (777) and (888). The growth of TDS correlates with the increase of the Cd transmission T(λ) in the range 0.2 < λ < 0.5 Å, which in the vicinity of (888) reflection is T(λ) ≈ 0.9. Therefore, the Cd shielding of the triple-bounce crystal becomes ineffective and the parasitic single-bounce back-face reflection and TDS, blocked for 0.5 < λ < 3.0 Å, reappear for λ< 0.5 Å.

It is practically impossible to separate this parasitic scattering from the triple-bounce reflection at steady state neutron beam lines except by the use of highly curved neutron guides. However, the TOF-USANS instrument, which is currently under construction at SNS, allows separation of the orders of Bragg reflections and the residual TDS in time-of-flight and thus the discovered parasitic effect cannot compromise its sensitivity. Thus, we expect to approach the theoretical limit of sensitivity for the SNS TOF-USANS instrument.

We describe ZEEMANS, a new instrument proposed for the Spallation Neutron Source (SNS) to probe matter at extremely high magnetic fields. The complexity of the high field magnet demands a versatile neutron scattering instrument, capable of performing diffraction (powder and single crystal), SANS, reflectometry, and inelastic spectrometry, with minimal modifications between configurations. In this paper we present a conceptual design for neutron scattering instrumentation to be built around the horizontal conical high field magnet. Monte Carlo simulations and analytical calculations indicate performance on a par with other SNS instrumentation despite limited access to the sample.

A fine resolution chopper spectrometer (SEQUOIA) recently received first neutrons at the SNS. The commissioning phase of the instrument is underway. SEQUOIA is designed to utilize neutrons of an incident energy (E_i) between 10-2000 meV. A monochromatic beam is provided on a sample, 20 m from the decoupled ambient temperature H₂O moderator, by filtering the white beam with a Fermi chopper located 18 m from the source. After interacting with the sample, neutrons are detected by an array of ³He linear position sensitive tubes located on a vertical cylinder with a radius of 5.5 m. This contribution presents current results from the commissioning experiments and compares SEQUOIA's actual and predicted performance. These commissioning experiments include characterization of the beam by monitors, determination of the chopper phase offsets, and runs with V and C₄H₂I₂S. The predicted performance is provided by analytical calculations and Monte Carlo simulations.

The novel BioRef reflectometer currently under construction in neutron guidehall-I of the BER-2 reactor at the Helmholtz Centre Berlin is designed for applications in soft matter science at solid-liquid interfaces especially under dynamic conditions. In addition to a time-of-flight (TOF) approach to be realised with three choppers in order to adapt resolutions and wavelength bands to the needs of specific applications, the instrument will be equipped with an in-situ infrared (IR) spectrometer operating in its surface sensitive ATR-geometry for simultaneous spectroscopic and conformational studies. The instrument will become operational in 2010.

The new multifunctional reflectometer GRAINS is under construction at the modernized high flux IBR-2 pulsed reactor (IBR-2M) of the FLNP JINR (Dubna, Russia). The principal feature of this reflectometer, the horizontal sample plane (or vertical scattering plane), enables the study of liquid-containing interfaces. The reflectometer will operate in the time-of-flight regime with constant sample illumination during measurements. The important advantage is the constant angular resolution with unvaried background. The additional modes of the GRAINS reflectometer comprise (1) off-specular scattering and GISANS, which are measured simultaneously in the TOF regime at a 2D position-sensitive detector; (2) angular encoding in the horizontal plane, which is provided by a Larmor precession region limited by current sheets in front of the sample; (3) 3D polarimetry in reflection, which is provided by a Larmor precession region around the sample position. The design of the reflectometer is optimised to take better advantage of an exceptionally broad wavelength band of the new cold moderator at the IBR-2M. The set-up will open up principally new possibilities for investigations in the field of interface nano-science at the IBR-2M reactor.

Small angle neutron scattering (SANS) instruments typically require a cold source and a large spread of wavelengths in order to enhance incident flux. However, as a direct result of the unavailability of a cold source at the Canadian Neutron Beam Centre (CNBC), we have resorted to adapting a triple-axis spectrometer for SANS measurements. This is achieved through the use of multiple converging incident beams which enhance the neutron flux on the sample by a factor of 20, compared to a single beam of same spot size. Furthermore, smearing effects due to vertical divergence from the slit geometry are reduced through the use of horizontal Soller collimators. As a result, this modified triple-axis spectrometer enables SANS measurements to a minimum q value (q_min) of 0.006 Å⁻¹ [1]. Data obtained from the modified triple-axis spectrometer are in good agreement with those data from the 30 m NG3-SANS instrument located at the National Institute of Standards and Technology (Gaithersburg, MD, USA).

The High Flux Isotope Reactor resumed operation in June of 2007 with a supercritical hydrogen cold source in horizontal beam tube 4. Cold guide 4 is a guide system designed to deliver neutrons from this source with a reasonable flux at wavelengths greater than 4 Å to several instruments, and includes a 15-m, 96-section, 4-channel bender. A time-of-flight spectrum with calibrated detector was recorded at port C of cold guide 4, and compared to McStas simulations, to generate a brightness spectrum.

Different options are considered to transport cold neutrons along 90 m for the proposed new spectrometer FIRES at the ISIS facility. Monte Carlo simulations using the McStas programme package are used to assess the performance of various guide designs from the biological shield to the sample position. By employing a curved geometry, to avoid the direct line of sight, a hybrid design which combines a curved ballistic guide and an elliptic focusing section appears to be the best solution.

We present the results of a virtual design study based on Monte-Carlo neutron ray tracing techniques for the neutron guide of the time of flight (TOF) spectrometer NEAT. We studied several configurations with linearly or elliptically tapered compressors with different degrees of focusing and different guide coatings. The calculations were performed and crosschecked using two software packages which produced similar results. The geometrical arrangement of selected guide components was optimised with the Particle Swarm Optimisation algorithm. The results of the Monte Carlo simulations confirm an expected intensity gain factor of approximately 5, that can be achieved by the optimal configuration.

The new research reactor at ANSTO (OPAL) is operating with seven neutron beam instruments in the user programme and three more under construction. The reactor design provides for expansion of the facility to eighteen instruments, and much of the basic infrastructure is already in place. However, an expansion of the neutron guide system is needed for further beam instruments. For this purpose, several possibilities are under consideration, such as insertion of multi-channel neutron benders in the existing cold guides or the construction of a new elliptic cold guide. In this work Monte Carlo (MC) simulations have been used to evaluate performance of these guide configurations. Results show that these configurations can be competitive with the best instruments in the world.

We have used SERGIS to probe the surface structure of a silicon diffraction grating of period 140 nm. Experiments were performed at: the Los Alamos Neutron Science Center (LANSCE) pulsed neutron source and the National Institute of Standards and Technology (NIST) continuous wave (CW) reactor neutron source. Although both sets of data show peaks of the spin echo polarization at integer multiples of the grating period, as expected, the results differ in detail. We have developed a dynamical theory, based on a Bloch wave expansion, to describe neutron diffraction from a grating. The theory explains the differences between the two sets of data without any adjustable parameters.

Fast intensity modulation techniques require neutron detectors with a response time below 1μs, a demand which can not be fulfilled by standard neutron detector technology. Here we present the CASCADE neutron detector developed at the University of Heidelberg, which is based on stacked, thin ¹⁰B layers as neutron converters and particularly addresses these needs. After explaining the CASCADE concept in context with fast intensity modulation techniques we report on two test runs performed at the RESEDA spectrometer at FRM II, Munich, which indeed prove MHz time resolution in this spectrometer system with a reasonably high detection efficiency.

Imaging with polarized neutrons is a new method to measure the spatially resolved magnetisation. It is based on the interaction of a polarized neutron beam with magnetic fields. In this paper we present an overview of different polarizing techniques and their application for neutron imaging. The performance of various setups is discussed. It is demonstrated that radiography with polarized neutrons may evolve into an important technique for determining the homogeneity of ferromagnetic samples.

Results of neutron transmission Bragg edge spectroscopic experiments performed at the SNAP beamline of the Spallation Neutron Source are presented. A high resolution neutron counting detector with a neutron sensitive microchannel plate and Timepix ASIC readout is capable of energy resolved two dimensional mapping of neutron transmission with spatial accuracy of ∼55 μm, limited by the readout pixel size, and energy resolution limited by the duration of the initial neutron pulse. A two dimensional map of the Fe 110 Bragg edge position was obtained for a bent steel screw sample. Although the neutron pulse duration corresponded to ∼30 mÅ energy resolution for 15.3 m flight path, the accuracy of the Bragg edge position in our measurements was improved by analytical fitting to a few mÅ level. A two dimensional strain map was calculated from measured Bragg edge values with an accuracy of ∼few hundreds μistrain for 300s of data acquisition time.

A pulsed neutron transmission coupled with a two-dimensional position sensitive neutron detector gives a time-of-flight spectrum at each pixel of the detector, which depends on the total cross-sections of materials. In order to extract quantitative information of the preferred orientation included in the Bragg scattering total cross-section data, a spectral analysis software for the 2D imaging has been developed, and the transmission data of an unbent iron plate were analyzed. The 2D images with respect to the preferred orientation were successfully obtained, and the effectiveness of spectroscopic neutron transmission imaging was indicated.

We study the effect of small angle scatterings on the interference-fringe contrast in a Jamin-type multilayer interferometer by performing a model calculation. Our calculation can be the basis for not only choosing the etalon bases of Jamin-type multilayer interferometer for very cold neutron but also analyzing quantitatively neutron dark-field tomography.

In the case of ultra small angle (neutron or x-ray) scattering (USANS, USAXS) it may happen that structures under investigations are not fully coherently illuminated by the incident wave. Despite this fact interference effects are observed similar to SAS data. In this case the measured scattering patterns must be different interpreted. We propose a procedure to calculate and adapt such scattering patterns to experimental data.

For a monochromatic neutron beam incident on a single crystal prism, we derived analytic expressions for variations of the deflection δ_cr and transmitted fraction I_O of forward diffracted neutrons, with the incidence angle θ. In the vicinity of a Bragg reflection, δ_cr deviates sharply from the deflection δ_am for an equivalent amorphous prism, reaching opposite extrema at either end of the total reflectivity domain and exhibits a 3 orders of magnitude greater sensitivity to θ than δ_am. We have experimentally observed the variation of δ_cr and I_O across a Bragg reflection for single crystal silicon prisms of various apex angles in several asymmetric Bragg configurations. The observed δ_cr deviates from δ_am by upto 27% with sensitivities |dδ_cr/dθ| upto 0.43 arcsec/arcsec. The results are in harmony with theory. This observation has led to the design of a super-collimator Bragg prism producing neutron beams with sub-arcsecond angular widths.

We have achieved the tightest collimation to date of a monochromatic neutron beam by diffracting neutrons from a Bragg prism, viz. a single crystal prism operating in the vicinity of Bragg incidence. An optimised silicon {111} Bragg prism has collimated 5.26Å neutrons down to 0.58 arcsecond. In conjunction with a similarly optimised Bragg prism analyser of opposite asymmetry, this ultra-parallel beam yielded a 0.62 arcsecond wide rocking curve. This beam has produced the first SUSANS spectrum in Q ∼ 10⁻⁶ Å⁻¹ range with a hydroxyapatite casein protein sample and demonstrated the instrument capability of characterising agglomerates upto 150 μm in size. The super-collimation has also enabled recording of the first neutron diffraction pattern from a macroscopic grating of 200 μm period. An analysis of this pattern yielded the beam transverse coherence length of 175 μm (FWHM), the greatest achieved to date for Å wavelength neutrons.

Multibeam focusing offers an appealing compromise between high resolution and high incident flux configurations for SANS spectrometers. In fact so many "spectrometers" operate in parallel as the number of channels in the collimator. Each channel provides high resolution by small spot size on the detector and long sample-to-detector distance, involving significant limitation of the transmitted beam phase space volume, thus reducing the flux. The flux on the sample is increased by the large number of channels. In view of the multibeam collimation it is beneficial to increase the beam cross section and decrease the divergence at the same time. Two aspects related to the use of rotational velocity selectors are investigated. First the transmitted phase space is determined from the selector parameters. It is found that the beam azimuthal divergence with respect to the rotor axis has a significant effect on the selectivity. Neutrons flying along different paths are treated differently, leading eventually to energetic non-uniformity of the illumination of various collimator channels. Then the effect of the gap in the neutron guide at the selector location on the phase space uniformity at the collimator entrance is investigated and optimal selector location along the beam is proposed together with optimal neutron guide shape in the vicinity of the gap, which accommodates the selector.

We have developed a 1-dimensional elliptic mirror combining a supermirror coated with ion-beam sputtering and precise elliptic surface figured with the numerically-controlled local wet etching process. In this study, NiC/Ti supermirror (m = 4) was deposited on a precisely figured surface of synthesized quartz glass over 90 mm × 40 mm. Wideband neutrons of λ > 3.64Å were focused with focal spot size down to 0.25 mm, peak intensity gain up to 6 without significant diffuse scattering. Time-of-flight measurements suggest that wideband neutrons are effectively focused to the focal point.

High-performance optical devices with a figure accuracy of sub-micrometer level and a surface roughness of atomic level are required to collect and/or to focus a neutron on a sample without scattering loss. To fabricate a high-performance neutron focusing supermirror, a two-stage numerically controlled local wet etching technique combined ion beam sputter deposition was developed. By applying this technique, a plano-elliptical substrate made of synthesized quartz glass with a figure accuracy of less than 0.5 μm was fabricated, and its surface was deposited with NiC/Ti multilayers by ion beam sputtering to produce an m=4 supermirror. The focusing performance of the supermirror was evaluated at the SUIREN of JRR-3M, and a focusing gain of 6 in peak intensity was achieved compared with a nonfocused direct beam.

A triplet magnetic lens system composed of three sextupole-magnets and two spin flippers was constructed to focus pulsed neutrons in a wide wavelength range with same focal lengths. In this study, we performed a pulsed neutron beam focusing experiment with the system. The design of the system and the experimental results are shown and discussed.

Conventionally, in time-of-flight (TOF) neutron spectroscopy neutron pulses of one single monochromatic wavelength are used. Repetition Rate Multiplication implies the use of a set of several monochromatic wavelengths coming from each source pulse, instead of a single one [1]. This makes it possible to overcome a major efficiency drawback of pulsed neutrons sources, i.e. the fact that the pulse repetition rate is too low for TOF spectroscopy, and allows us to freely choose the pulse repetition rate at the sample. The Repetition Rate Multiplication method was first developed in the framework of the IN500 project at LANSCE (USA) [2] and has in the meantime been implemented at several projects at ISIS (UK) [3] and J-PARC [4]. Here we describe the application of the Repetition Rate Multiplication method to hot, thermal and cold neutron scattering by using fixed and wavelength dependent pulse suppression. Further we present the first experimental realization of this novel technique using the flexible disc chopper system of the TOF spectrometer NEAT at BENSC.

The new wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source at Oak Ridge National Laboratory has been successfully used in white-beam mode, with no Fermi chopper, to obtain neutron powder diffraction based atomic pair distribution functions (PDFs). Obtained PDF patterns of Si, Ni, and Al₂O₃ were refined using the PDFfit method and the results compared to data collected at the NPDF diffractometer at Los Alamos National Laboratory. High quality resulting fits are presented, demonstrating that reliable powder diffraction data can be obtained from ARCS when operated in this configuration.

We present a new polarizing system built for the relocated wide angle Neutron Spin Echo instrument SPAN. The new instruments at the second Guide Hall of BENSC and the relocation of SPAN to this hall of BENSC required a new beam extraction system and a new polarizer for SPAN, which replaced the old beam splitter produced in 1994 with FeCo-Si supermirrors with m=2. The new polarizer uses Fe-Si supermirrors, which do not run the risk to become activated as the old FeCo-Si supermirrors and was designed to deliver a polarized beam for wavelengths above 2.5 Å. The final polarizing cavity has a length of 9 m with a cross section of 60 mm × 100 mm. Si wafers coated on both sides with m=2.5 Fe-Si polarizing supermirrors are glued into the guide at an angle of 0.38° to the walls.

The guide was installed during the second half year of 2006 and the first tests in early 2007 revealed excellent polarization efficiency over the whole wavelength range of the spectrometer of 2.5 Å to 9 Å, amounting to above 95% at 4.5 Å.

Recently, we have developed an optimized process for polishing Al substrates leading to an extraordinary low surface roughness comparable to float glass of high quality. Indeed, supermirror coatings with R = 91% at the critical angle of reflection of m = 2 were produced demonstrating the excellent quality of the Al surface. Supermirror coated Al substrates open new options for advanced neutron optical devices. As one example neutron guides can start very close from the moderator. We investigated this option by Monte-Carlo simulations for i) a conventional, curved guide and ii) an elliptic guide. In case of i) an increase of flux at long wavelengths is obtained because of complete illumination of the phase space accepted by the guide. The elliptic guide starting close to the moderator (ii) has significantly enhanced neutron transport properties since only useful neutrons are extracted and transported to the sample. As a result such a guide concept is superior in terms of flux when compared with a conventional guide system and in terms of signal to background and well defined beam focusing compared with an elliptic guide starting at a larger distance from the moderator. In particular, experiments on novel materials, which are often only available in small quantities or samples under extreme conditions will profit from neutron beams of such high quality.

IBARAKI Materials Design Diffractometer (iMATERIA) is a high-throughput powder diffractometer. iMATERIA has a vacuum chamber, which is enclosed in a shield. Each sample is measured in 10 minutes, and must be placed in the vacuum chamber before being measured. If the vacuum in the chamber cannot be maintained while exchanging samples, the process of re-establishing the vacuum would become a bottleneck when samples are exchanged. To reduce exchange time, we developed and manufactured an automatic sample changer that can handle a large number of samples (up to 672) through both the vacuum chamber and shielding blocks.

A precise, versatile, and automated method of orienting a sub-millimeter crystal in a focused neutron beam is required for efficient operation of the TOPAZ Single Crystal Diffractometer at the Spallation Neutron Source at Oak Ridge National Laboratory. To fulfill this need, a Compact Crystal Positioning System (CCPS) has been developed in collaboration with Square One Systems Design in Jackson, Wyoming. The system incorporates a tripod design with six vacuum-compatible piezoelectric linear motors capable of < 1μm resolution. National Instruments LabVIEW provides a means of system automation while at the same time accommodating the modular nature of the SNS sample environment control software for straightforward system integration. Results from an ambient test at the Advanced Photon Source at Argonne National Laboratory will be presented.

A low temperature sample orientation device providing three axes of rotation has been successfully built and is in testing for use on several spectrometers at the spallation neutron source (SNS). Sample rotation about the vertical (ω) axis of nearly 360° and out of plane tilts (ϕ and v) of from -3.4° to 4.4° and from -2.8° to 3.5°, respectively, are possible. An off-the-shelf closed cycle refrigerator (CCR) is mounted on a room temperature sealed rotary flange providing ω rotations of the sample. Out-of-plane tilts are made possible by piezoelectric actuated angular positioning devices mounted on the low temperature head of the CCR. Novel encoding devices based on magnetoresistive sensors have been developed to measure the tilt stage angles. This combination facilitates single crystal investigations from room temperature to 3.1 K. Commissioning experiments of the rotating CCR for both powder and single crystal samples have been performed on the ARCS spectrometer at the SNS. For the powder sample this device was used to continuously rotate the sample and thus average out any partial orientation of the powder. The powder rings observed in S(Q) are presented. For the single crystal sample, the rotation was used to probe different regions of momentum transfer (Q-space). Laue patterns obtained from a single crystal sample at two rotation angles are presented.

We report here the construction and neutron transmission test results of an in-situ polarized ³He-based neutron polarization analyzer system for the Magnetism Reflectometer at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyzer uses the Spin-Exchange Optical Pumping method to polarize the ³He nuclei of a cell of ³He gas. Polarized neutrons scattered from the sample are intercepted by the polarized ³He gas which strongly absorbs neutrons in one spin-state while allowing most neutrons in the other spin-state to pass through. To maintain a stable analyzing efficiency during an experiment, the ³He gas is continuously polarized in-situ on the instrument. Neutron transmission measurements showed that 73% ³He polarization was reached in this setup.

Development of neutron spin filters based on polarized ³He is underway at Spallation Neutron Source (SNS). We report the progress of electrical heating tests in polarized ³He based on Spin-Exchange Optical Pumping (SEOP) method. We first test the system performance based on electrical heating via non-inductance heating pads. We observe a contribution of 955 hours to the relaxation time T₁ from the heating pads. We then test the electrical heating SEOP pumping system at the SNS beamline Magnetic Reflectometer. We currently obtain 73% ³He polarization in a cell with 820 cm³ in volume.

We report on the progress of the Dynamically Polarized Sample at the Spallation Neutron Source. The SNS DPS is a collaborative project with the University of Virginia constructed for the purpose of polarized neutron scattering and diffraction. The project aims at significantly enhancing the signal-to-noise ratio by utilizing the strong spin dependent scattering cross section of hydrogen. One of the areas that are expected to benefit from this project is neutron protein crystallography, where a 10 fold gain in diffraction intensity and 10 fold reduction in incoherent background are within reach. The first step of the SNS DPS project uses a simple one Kelvin refrigerator and a 5 Tesla magnet. Our final goal is to design and build optimized setups for instruments such as the neutron protein diffractometer at the SNS (MaNDi). A brief overview of the DPS project will be given.

In an effort to mitigate the expense and broaden the applicability of customised environment chambers, researchers at the University of Melbourne and the Australian Nuclear Science and Technology Organisation (ANSTO) have designed and are currently commissioning a modular reaction chamber, capable of separating the necessities of diffraction methodologies from those of the desired sample environment. The In Situ Reaction Chamber (ISRC) abstracts many of the details intrinsic to the diffractometer, allowing users to design inexpensive environmental inserts that may be readily customised to their individual needs. The first insert to be developed for use with the ISRC is a high temperature furnace capable of providing an oxidising sample environment up to 1600°C.

A flow-through quartz gas cell, together with a gas flow control and monitoring system, has been designed and constructed at ISIS. This equipment allows neutron powder diffraction data to be collected on samples at temperatures up to around 1300 K when exposed to user chosen mixtures of O2, Ar, CO2, and CO. By exploiting the sensitivity of neutrons to the presence of light atoms such as oxygen, it is possible to probe the crystal structure of oxide materials as a function of oxygen partial pressures down to log₁₀p(O₂) of about −20. The resultant structural information can then be correlated with the bulk properties of the materials, whose research and technological interests lie in fields such as energy production, storage materials, catalysis, and earth science.

A high pressure, high temperature sapphire cell has been designed to provide users at the Spallation Neutron Source with the ability to perform in-situ supercritical bulk water studies. The design criteria for the cell required the achievement of a maximum pressure of 150 MPa at the maximum temperature of 500°C. Other conceptual constraints, such as a 360° viewing angle and top loading integration further complicated and limited available cell models. The sapphire cell was tested and modified due to pre-mature failure. Due to convenient geometry and ease of operation, interest in the cell for more moderate operating requirements has increased.

Cryogenic equipment can be found in the majority of neutron scattering experiments. Recent increases in liquid helium cost caused by global helium supply problems lead to significant concern about affordability of conventional cryogenic equipment. However the latest progress in cryo-cooler technology offers a new generation of cryogenic systems in which the cryogen consumption can be significantly reduced and in some cases completely eliminated. These systems also offer the advantage of operational simplicity, require less space than conventional cryogen-cooled systems and can significantly improve user safety. At the ISIS facility it is possible to substitute conventional cryostats with cryogen free systems. Such systems are based on the pulse tube refrigerator (PTR) which possesses no cold moving parts. Oxford Instruments in collaboration with ISIS have developed new high magnetic field sample environment equipment based on re-condensing technology. This project includes 9T wide angle chopper magnet for spectrometry and 14T magnet for diffraction. The main advantage of these systems is that all magnet operating procedures, for example cooling, running up to the field and quenching remain the same as for a standard magnet in a bath cryostat. This approach also provides a homogeneous temperature distribution, which is crucial for optimum magnet performance.

The majority of superconducting magnets for neutron scattering experiments take the form of split pairs with magnetic field vector in the vertical plane. Sample environment access is along the vertical magnetic axis whilst neutron access is in the horizontal plane. Split pair superconducting magnets present significantly more challenges in terms of design than the simpler solenoid type arrangement and the addition of requirements for neutron access further complicates the situation. Many of the requirements of split pair magnets for neutron scattering are conflicting and often compromises have to be made. Presented here are some of the more important design criteria and the ways in which these are met in practical magnet designs. Topics covered range from the choice of superconducting material through to the control of magnetic flux density profiles and mechanical aspects of the magnet former providing the neutron access between the coils. Most of the information presented is based on recent or current production magnets manufactured by Oxford Instruments for a range of neutron related applications.

The efficient use of complex neutron scattering instruments is often hindered by the complex nature of their operating software. This complexity exists at each experimental step: data acquisition, reduction and analysis, with each step being as important as the previous. For example, whilst command line interfaces are powerful at automated acquisition they often reduce accessibility by novice users and sometimes reduce the efficiency for advanced users. One solution to this is the development of a graphical user interface which allows the user to operate the instrument by a simple and intuitive "push button" approach. This approach was taken by the Motofit software package for analysis of multiple contrast reflectometry data. Here we describe the extension of this package to cover the data acquisition and reduction steps for the Platypus time-of-flight neutron reflectometer. Consequently, the complete operation of an instrument is integrated into a single, easy to use, program, leading to efficient instrument usage.

Large-scale neutron facilities such as the Spallation Neutron Source (SNS) located at Oak Ridge National Laboratory need easy-to-use access to Department of Energy Leadership Computing Facilities and experiment repository data. The Orbiter thick- and thin-client and its supporting Service Oriented Architecture (SOA) based services (available at https://orbiter.sns.gov) consist of standards-based components that are reusable and extensible for accessing high performance computing, data and computational grid infrastructure, and cluster-based resources easily from a user configurable interface. The primary Orbiter system goals consist of (1) developing infrastructure for the creation and automation of virtual instrumentation experiment optimization, (2) developing user interfaces for thin- and thick-client access, (3) provide a prototype incorporating major instrument simulation packages, and (4) facilitate neutron science community access and collaboration. The secure Orbiter SOA authentication and authorization is achieved through the developed Virtual File System (VFS) services, which use Role-Based Access Control (RBAC) for data repository file access, thin-and thick-client functionality and application access, and computational job workflow management. The VFS Relational Database Management System (RDMS) consists of approximately 45 database tables describing 498 user accounts with 495 groups over 432,000 directories with 904,077 repository files. Over 59 million NeXus file metadata records are associated to the 12,800 unique NeXus file field/class names generated from the 52,824 repository NeXus files. Services that enable (a) summary dashboards of data repository status with Quality of Service (QoS) metrics, (b) data repository NeXus file field/class name full text search capabilities within a Google like interface, (c) fully functional RBAC browser for the read-only data repository and shared areas, (d) user/group defined and shared metadata for data repository files, (e) user, group, repository, and web 2.0 based global positioning with additional service capabilities are currently available. The SNS based Orbiter SOA integration progress with the Distributed Data Analysis for Neutron Scattering Experiments (DANSE) software development project is summarized with an emphasis on DANSE Central Services and the Virtual Neutron Facility (VNF). Additionally, the DANSE utilization of the Orbiter SOA authentication, authorization, and data transfer services best practice implementations are presented.

In a busy world, continuing with the status-quo, to do things the way we are already familiar, often seems to be the most efficient way to conduct our work. We look for the value-add to decide if investing in a new method is worth the effort. How shall we evaluate if we have reached this tipping point for change? For contemporary researchers, understanding the properties of the data is a good starting point. The new generation of neutron scattering instruments being built are higher resolution and produce one or more orders of magnitude larger data than the previous generation of instruments. For instance, we have grown out of being able to perform some important tasks with our laptops – the data are too big and the computations would simply take too long. These large datasets can be problematic as facility users now begin to grapple with many of the same issues faced by more established computing communities. These issues include data access, management, and movement, data format standards, distributed computing, and collaboration among others. The Neutron Science Portal has been architected, designed, and implemented to provide users with an easy-to-use interface for managing and processing data, while also keeping an eye on meeting modern cybersecurity requirements imposed on institutions. The cost of entry for users has been lowered by utilizing a web interface providing access to backend portal resources. Users can browse or search for data which they are allowed to see, data reduction applications can be run without having to load the software, sample activation calculations can be performed for SNS and HFIR beamlines, McStas simulations can be run on TeraGrid and ORNL computers, and advanced analysis applications such as those being produced by the DANSE project can be run. Behind the scenes is a "live cataloging" system which automatically catalogs and archives experiment data via the data management system, and provides proposal team members access to their experiment data. The complexity of data movement and utilizing distributed computing resources has been taken care on behalf of users. Collaboration is facilitated by providing users a read/writeable common area, shared

The unique contributions of the Neutron Science TeraGrid Gateway (NSTG) are the connection of national user facility instrument data sources to the integrated cyberinfrastructure of the National Science FoundationTeraGrid and the development of a neutron science gateway that allows neutron scientists to use TeraGrid resources to analyze their data, including comparison of experiment with simulation. The NSTG is working in close collaboration with the Spallation Neutron Source (SNS) at Oak Ridge as their principal facility partner. The SNS is a next-generation neutron source. It has completed construction at a cost of $1.4 billion and is ramping up operations. The SNS will provide an order of magnitude greater flux than any previous facility in the world and will be available to all of the nation's scientists, independent of funding source, on a peer-reviewed merit basis. With this new capability, the neutron science community is facing orders of magnitude larger data sets and is at a critical point for data analysis and simulation. There is a recognized need for new ways to manage and analyze data to optimize both beam time and scientific output. The TeraGrid is providing new capabilities in the gateway for simulations using McStas and a fitting service on distributed TeraGrid resources to improved turnaround. NSTG staff are also exploring replicating experimental data in archival storage. As part of the SNS partnership, the NSTG provides access to gateway support, cyberinfrastructure outreach, community development, and user support for the neutron science community. This community includes not only SNS staff and users but extends to all the major worldwide neutron scattering centers.