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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Neutronic engine

An internal combustion engine for neutron diffraction analysis is provided. The engine includes an elongated piston chamber formed from an aluminum alloy to ensure maximum neutron visibility into the combustion chamber. An elongated piston assembly reciprocates within the elongated piston chamber, the piston assembly including an upper piston joined to a lower piston. The upper piston and the lower piston are hollow, thereby reducing the reciprocating mass and increasing neutron access to the combustion chamber. The upper piston is lubricated with a neutron-transparent fluorocarbon lubricant such as perfluoropolyether (PFPE), while the lower piston and the crankcase are lubricated with hydrocarbon lubricant. The engine enables 3D and time-resolved measurements of strain, stress, and temperature, as well as phase transformation, texture, and microstructure.

Wissink, Martin L.↗
DOE OSTI2026

Thermal neutron imaging detector with wavelength shifting fiber and digital readout

Here, we developed a large area, digital thermal neutron imaging detector. The detector uses a 6 LiF/ZnS(Ag) neutron-sensitive scintillator combined with wavelength shifting fiber technology. The signals from fiber channels are amplified, integrated, and digitized using individual analog-to-digital converters for each channel. The neutron position is determined from the digitized signal using a least-squares gaussian-fitting algorithm. The detector size was 77 × 38 cm 2 (2926 cm 2 ), it provided 1.3 mm resolution, and its resolution can further be improved. The detector was designed for a powder diffraction neutron scattering beamline and provided substantial improvement of d-space resolution compared with existing detectors. This detector may have broader applications due to its large area and high spatial resolution extended over its large area.

6LiF/ZnS(Ag) scintillator↗
DOE OSTI2020

Unprecedented non-hysteretic superelasticity of [001]-oriented NiCoFeGa single crystals

Superelasticity associated with the martensitic transformation has found a broad range of engineering applications. However, the intrinsic hysteresis and temperature sensitivity of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. In this paper, we report a large superelasticity up to 15.2% strain in [001]-oriented NiCoFeGa single crystals, exhibiting non-hysteretic mechanical responses, a small temperature dependence and high-energy-storage capability and cyclic stability over a wide temperature and composition range. In situ synchrotron X-ray diffraction measurements show that the superelasticity is correlated with a stress-induced continuous variation of lattice parameter accompanied by structural fluctuation. Neutron diffraction and electron microscopy observations reveal an unprecedented microstructure consisting of atomic-level entanglement of ordered and disordered crystal structures, which can be manipulated to tune the superelasticity. The discovery of the large elasticity related to the entangled structure paves the way for exploiting elastic strain engineering and development of related functional materials. NiCoFeGa single crystals exhibit large non-hysteretic superelasticity over broad temperature and composition ranges. It is attributed to the continuous phase transition with applied stress, which is related to the fluctuation of entangled ordered and disordered crystal structures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Demonstration of neutron time-of-flight diffraction with an event-mode imaging detector

Neutron diffraction beamlines have traditionally relied on deploying large detector arrays of 3 He tubes or neutron-sensitive scintillators coupled with photomultipliers to efficiently probe crystallographic and microstructure information of a given material. Given the large upfront cost of custom-made data acquisition systems and the recent scarcity of 3 He, new diffraction beamlines or upgrades to existing ones demand innovative approaches. This paper introduces a novel Timepix3-based event-mode imaging neutron diffraction detector system as well as first results of a silicon powder diffraction measurement made at the HIPPO neutron powder diffractometer at the Los Alamos Neutron Science Center. Notably, these initial measurements were conducted simultaneously with the 3 He array on HIPPO, enabling direct comparison. Data reduction for this type of data was implemented in the MAUD code, enabling Rietveld analysis. Results from the Timepix3-based setup and HIPPO were benchmarked against McStas simulations, showing good agreement for peak resolution. With further development, systems such as the one presented here may substantially reduce the cost of detector systems for new neutron instrumentation as well as for upgrades of existing beamlines.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Status Report on Development of a Cask to Enable Pulsed Neutron Characterization of Irradiated Fuel

We present the design of a shielding cask that allows pulsed neutron characterization of irradiated fuel rodlets prior to their destructive examination in hot cells. The goal is to provide complementary and informative measurements that will inform subsequent hot cell PIE examinations by identifying typical and atypical regions with respect to microstructure, tomographic data, or isotope densities. Time-of-flight neutron diffraction has the potential to offer efficient, non-destructive and non-contact microstructural characterization of irradiated fuel pins with spatial resolution of 1 mm3 to 1 cm3 while for energy-resolved neutron imaging (and by extension tomography) a resolution of 100 μm was demonstrated. The potential results include crystallinity vs. amorphous volumes and microstructural information such as phase compositions and textures from the diffraction data as well as distances (e.g. pellet to cladding), cracks, and isotopic distributions of minor actinides, fission products as well as fission gas partial pressures e.g. in the plenum from energy resolved neutron imaging. The capability will identify regions of atypical behavior and provide cost effective bulk characterization of entire samples prior to destructive evaluation in hot cells. This effort is a collaboration between LANL, INL, ORNL, and UC Berkeley. A key facet of the initiative is the ability to cost effectively ship irradiated fuels from INL to the pulsed spallation neutron source at LANSCE. The irradiated fuel would be loaded in the custom designed cask (designated RaMHaM) at INL hot cells which then could be shipped in a BRR Type B shipment container between INL and LANL. No hot cell is required after the loading of the sample at INL in the pathway laid out in this report, greatly simplifying handling at LANL.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

X-Ray Diffraction of Slag-Based Sodium Salt Waste Forms

Cementitious materials are used to solidify and stabilize aqueous based radioactive waste containing sodium salts. The types and proportions of cementitious ingredients used to treat aqueous radioactive waste streams containing sodium salts depend on the performance objectives for the waste forms and the compositions of the waste streams. Matrix phases can stabilize certain contaminants (co-precipitation, substitution, ion exchange, and / or sorption), influence processing properties, and are responsible for physical properties and durability of the cured waste forms. Consequently, characterization of the matrix (binder) mineralogy (chemical compositions and crystalline / non crystalline structures) is important for predicting contaminant leaching and evolution of the materials as a function of time and changing conditions This report documents sample preparation and x-ray diffraction results for a series of mixtures of sodium salt waste and cementitious binders. The objective of this study was to provide initial phase characterization for the CBP reference case cementitious salt waste form. This information can be used to: 1) generate a base line for the evolution of the waste form as a function of time and conditions, 2) potentially to design new binders based on mineralogy of the binder, 3) understand and predict anion and cation leaching behavior of contaminants of concern, and 4) predict performance of the waste forms for which phase solubility and thermodynamic data are available. Characterization of the mineralogy is also important for understanding the buffering effects that the waste form has on infiltrating water / leachates. More specifically, identification of hydrated phases capable of sequestering anions in the structures and crystallinity of the calcium silicate binder phases were of particular interest. The intent was to use this characterization data as a starting point for more detailed phase characterization using neutron diffraction techniques in addition to quasi-elastic neutron scattering techniques for characterization of water at the ORNL Spallation Neutron Source, Oak Ridge, TN. The initial characterization is complete. Due to extensive substitutions of cations and anions in the layered double hydroxide phases and the very fine intermixing of poorly crystalline hydrated phases in the reference case blend (10 : 45 : 45 cement : slag : fly ash), electron diffraction and transmission electron spectroscopy are recommended as the next step for characterization. In summary, the hydrated mixtures of Type II portland cement, Grade 100 ground granulated blast furnace slag (GGBFS) and carbon burn-out (CBO) Class F Fly ash contained hydrated phase assemblages which were typical of those reported in the literature. Based on x-ray diffraction results, no significant differences were detected in samples cured 2 months and 14 months in sealed containers at ambient indoor temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structure and properties of densified silica glass: characterizing the order within disorder

The broken symmetry in the atomic-scale ordering of glassy versus crystalline solids leads to a daunting challenge to provide suitable metrics for describing the order within disorder, especially on length scales beyond the nearest neighbor that are characterized by rich structural complexity. Here, we address this challenge for silica, a canonical network-forming glass, by using hot versus cold compression to (i) systematically increase the structural ordering after densification and (ii) prepare two glasses with the same high-density but contrasting structures. The structure was measured by high-energy X-ray and neutron diffraction, and atomistic models were generated that reproduce the experimental results. The vibrational and thermodynamic properties of the glasses were probed by using inelastic neutron scattering and calorimetry, respectively. Traditional measures of amorphous structures show relatively subtle changes upon compacting the glass. The method of persistent homology identifies, however, distinct features in the network topology that change as the initially open structure of the glass is collapsed. The results for the same high-density glasses show that the nature of structural disorder does impact the heat capacity and boson peak in the low-frequency dynamical spectra. Densification is discussed in terms of the loss of locally favored tetrahedral structures comprising oxygen-decorated SiSi 4<:sub> tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Deviation from the dipole-ice model in the spinel spin-ice candidate MgEr 2 Se 4

In spin-ice research, small variations in structure or interactions drive a multitude of different behaviors, yet the collection of known materials relies heavily on the “227” pyrochlore structure. Here, we present thermodynamic, structural, and inelastic-neutron-scattering data on a spin-ice material, MgEr 2 Se 4 , which contributes to the relatively underexplored family of rare-earth spinel chalcogenides. X-ray and neutron diffraction confirm a normal spinel structure and place Er 3+ moments on an ideal pyrochlore sublattice. Measurement of crystal electric field excitations with inelastic neutron scattering confirms that the moments have perfect Ising character, and further identifies the ground-state Kramers doublet as having dipolar-octupolar form with a significant multipolar character. Heat capacity and magnetic neutron diffuse scattering have icelike features, but are inconsistent with Monte Carlo simulations of the nearest-neighbor and next-nearest-neighbor dipolar spin-ice (DSI) models. A significant remnant entropy is observed as T → 0 K, but again falls short of the full Pauling expectation for DSI, unless significant disorder is added. We show that these observations are fully in line with what has been recently reported for CdEr 2 Se 4 , and point to the importance of quantum fluctuations in these materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of Abrasive Grinding on Through-Section Residual Stresses on Bearing Steel

In today’s industrial world, bearings are used in traditional applications such as automotive, steel mills, paper mills, railways as well as high precision applications such as aerospace, medical, renewable energy etc. Regardless of application, residual stresses play an important role in the service life of a bearing. In general, bearings experience Hertzian stresses in the order of 2-3 GPa with maximum stresses generated in the subsurface. Depending upon the magnitude and nature (tensile or compressive), the residual stresses enhance or reduce the application stresses. The residual stresses are generated during each stage of manufacturing process. For bearing components, the manufacturing stages include – tube rolling, green machining followed by heat treatment and final finishing. Majority of bearings are finished using abrasive grinding to achieve the final size and shape. The work holding and material removal during the grinding process can cause significant distortion. Distortion of bearing components is ab significant issue, especially for thin sectioned components, leading to high scrap rates. In this study, diffraction was utilized to understand the evolution of through thickness residual stresses after abrasive grinding on a thin walled bearing component. The results from neutron diffraction were coupled with distortion measurement especially the out of roundness to understand the effect of the final processing on the residual stress state present in the bearings.

Bedekar, Vikram↗
DOE OSTI2025

RICH (Robotic Interface Control & Handling) System for VULCAN

High flux neutron beam and high efficiency detectors warrant quick turn arounds of neutron diffraction measurements at the engineering materials diffractometer VULCAN. Efficient change and alignment of samples and automatic measurements at VULCAN are desired for better use of neutron beam time by users. In this work, we aim to develop a proof-of-concept Robotic Interactive Control & Handling System (RICH) for sample handling at VULCAN that could assist high throughput experiments and reduce the overhead time significantly. This was realized by a six-axis desktop robot with trained AI models. The trained AI models can recognize and locate samples in various types of positions in a live video stream. In addition, we developed smart algorithms which used our models on multiple cameras to recognize where samples are with respect to multiple point of views, and then using user-inputted parameters, align them to perform complex measurements.

42 ENGINEERING↗
DOE OSTI2014

Observations of a dynamical-to-kinematic diffraction transition in plastically deformed polycrystalline intermetallic YCu

Unlike most intermetallic compounds, polycrystalline YCu, a B2 (CsCl-type) intermetallic, is ductile at room temperature. The mechanisms for this behavior are not fully understood. In situ neutron diffraction was used to investigate whether a stress-induced phase transformation or twinning contribute to the ductility; however, neither mechanism was found to be active in YCu. Surprisingly, this study revealed that the intensities of the diffraction peaks increased after plastic deformation. It is thought that annealing the samples created nearly perfect crystallinity, and subsequent deformation reduced this high degree of lattice coherency, resulting in a modified mosaic structure that decreased or eliminated the extinction effect. Analysis of changes in diffraction peak intensity showed a region of primary plasticity that exhibits significant changes in diffraction behavior. Fully annealed samples initially contain diffracting volumes large enough to follow the dynamical theory of diffraction. When loaded beyond the yield point, dislocation motion disrupts the lattice perfection, and the diffracting volume is reduced to the point that diffraction follows the kinematic theory of diffraction. Since the sample preparation and deformation mechanisms present in this study are common in numerous material systems, this dynamical to kinematic diffraction transition should also be considered in other diffraction experiments. These measurements also suggest the possibility of a new method of investigating structural characteristics. (C) 2014 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Crystallographic and magnetic properties of the spinel-type ferrites Zn{sub x}Co{sub 1-x}Fe{sub 2}O{sub 4} (0.0 ≤ x ≤ 0.75)

Ultrahigh frequencies (UHF) have applications in signal and power electronics to minimize product sizes, increase production quantity and lower manufacturing cost. In the UHF range of 300 MHz to 3 GHz, ferrimagnetic iron oxides (ferrites) are especially useful because they combine the properties of a magnetic material with that of an electrical insulator. Ferrites have much higher electrical resistivity than metallic ferromagnetic materials, resulting in minimization of the eddy current losses, and total penetration of the electromagnetic (EM) field. Hence ferrites are frequently applied as circuit elements, magnetic storage media like read/write heads, phase shifters and Faraday rotators. The electromagnetic properties of ferrites are affected by operating conditions such as field strength, temperature and frequency. The spinel system Zn{sub x}Co{sub 1-x}Fe{sub 2}O{sub 4} (x=0.0, 0.25, 0.50 and 0.75) has been prepared by the standard solid state sintering method. X-ray and neutron powder diffraction measurements were performed at room temperature. Neutron diffraction data analysis confirms the cubic symmetry corresponding to the space group Fd3m. The distribution of three cations Zn{sup 2+}, Co{sup 2+} and Fe{sup 3+} over the spinel lattice and other crystallographic parameters like lattice constant, oxygen position parameter, overall temperature factor and occupancies of different ions in different lattice sites for the samples have been determined from the analysis of neutron diffraction data. The lattice constant increases with increasing Zn content in the system. The magnetic structure was found to be ferrimagnetic for the samples with x≤0.50. Magnetization measurements show that with the increase of Zn content in the system the value of saturation magnetization first increases and then decreases. The variation of the magnetic moment with Zn substitution has been discussed in terms of the distribution of magnetic and non-magnetic ions over the A and B sub-lattices and their exchange coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Complex Structural Disorder in a Polar Orthorhombic Perovskite Observed through the Maximum Entropy Method/Rietveld Technique

Ambient pressure stable perovskite oxides with all Bi3+ on the A-site are rare, with only four examples known. Due to the lone pair on Bi 3+ , these materials are seen as the best alternative to Pb-based piezoelectrics, which are used widely in society. The industry standard piezoelectric, Pb (Zr 1 – x Ti x )O 3 , relies on the [001] polarization of PbTiO 3 , but there are currently no ambient pressure stable Bi-based perovskites with this polarization vector, preventing the creation of an analogous system. We present the full structural analysis of the orthorhombic phase of (1 – x)Bi (Ti 3/8 Fe 2/8 Mg 3/8 )O 3 – x CaTiO 3 , which crystallizes in Pna2 1 symmetry with [001] polarization. This symmetry is rare and has only been reported twice for perovskites at ambient conditions. Analysis of maximum entropy method (MEM) models using synchrotron radiation powder X-ray diffraction reveals a disordered A-site configuration, and the MEM/Rietveld technique generates a structural model of this extreme disorder. Combined Rietveld analysis of X-ray and neutron diffraction data yields an accurate description of the local A-site configuration, which we use to understand our dielectric, ferroelectric, and piezoelectric measurements. These results give insight into how to stabilize this unique symmetry and inspire new design principles for Bi-based piezoelectrics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Complete Status Report Documenting the Development of Friction Stir Welding for Producing a Butt Joint in Thin Wall Tubing of ODS Alloys

A challenging attempt using friction stir welding to produce a butt joint between two 1.0 mm thick plates of 14YWT was nearly successful. The modified tool pin mostly penetrated the thickness of the adjoined thin plate samples resulting in a small blunt notch on the bottom surface of the butt joint. A bend occurred in the thin plate sample due to formation of stresses from clamping the thin plate sample during FSW. The peak displacement of the bend occurred along the center line of the butt joint. The weld zone showed good microstructure mixing with some flashing mostly on the retreating side that suggested excess heat input by friction between the traveling and spinning tool pin and thin plates of 14YWT. Neutron diffraction experiments were performed on the bent sample of 14YWT to measure the residual stresses in the butt joint on the HB-2B beam line at the Neutron Residual Stress Facility at HFIR. However, the neutron scattering to background noise ratio was very low during data acquisition. Measurements of lattice strains were obtained in the rolling (RD) and normal (ND) directions but not in the extrusion direction (ED) of the thin plate sample. Unfortunately, the quality of the data was not sufficient for determining the residual stresses in the butt joint. From the previous neutron scattering experiments conducted on four hot rolled plates (R1, R2, R3 and R4) of 14YWT, the residual stresses were calculated from lattice strain data and plotted in 2-D color contour maps for ED, RD and ND. The results showed variations in the magnitude and spatial position of residual stresses in the microstructure of the four plates. The magnitude in residual stresses in ED and RD increased gradually with increasing rolling deformation for R1 (50%) to R2 (76%), followed by larger increases in R3 (89%) and R4 (95%). The maximum peaks in residual stresses for R4 was ~710-730 MPa in ED and RD. The residual stresses in ND were below ~300 MPa for each of the 4 rolled plates, with a maximum residual stress in R4 (95%) of ~400 MPa. These results indicated that significant residual stresses representing ~57% of the yield stress of 14YWT (SM13) had accumulated in the 14YWT plate after hot rolling to the 1 mm thickness, which was used in the FSW experiments. The microstructure analysis of the 1.0 mm thick plate of 14YWT containing the butt joint produced by FSW revealed significant changes in the grain structure and texture between the unaffected zone (UZ) of the rolled plate and the butt joint weld. In the UZ, the grains were severely elongated after 95% deformation and mainly possessed the {101} texture component in the ED. Two predominant grain misorientation angles were observed: one consisting of small misorientations of <5º between highly elongated grains and the other consisting of large misorientations of >15º in pockets of small grains that might have formed by dynamic recrystallization processes during rolling of the plate at 1000ºC. The morphology and texture of grains in the heat affected zone (HAZ) were similar to those in UZ, except the grains had coarsened due to excess heat input during FSZ. A population of pores formed and the grains both coarsened and changed to isotropic morphology in the microstructure of the butt joint on both the advancing and retreating sides. The texture of grains in both regions were randomly orientated between the 3 poles {001}, {101} and {111}. The main difference in texture of grains between the advancing side and retreating side was with the misorientation angles of neighboring grains. Most of the grains in the advancing side had misorientation angles of >5º indicating that these grains experienced recrystallization. On the retreating side, areas containing larger grains showed high misorientation angles of >15º compared to areas appearing as bands of grains with misorientation angles of <5º and between 5º-15º. Numerous small pockets of grains with low misorientation angles of <5º were distributed in the microstructure among the grains showing high misorientation angles of >15º. It was determined that the grains associated with low misorientation angles contained sub-grain structures, which was consistent with both recrystallization and recovery mechanisms for grains located on the retreating side of the butt joint. These results demonstrate the complex microstructure that evolves in the microstructure of 14YWT resulting from the input of high temperatures and severe deformations during FSW.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Magnetic structures and interplay between rare-earth Ce and Fe magnetism in single-crystal CeFeAsO

Neutron and synchrotron resonant x-ray magnetic scattering (RXMS) complemented by heat capacity and resistivity measurements reveal the evolution of the magnetic structures of Fe and Ce sublattices in a CeFeAsO single crystal. The RXMS of magnetic reflections at the Ce L II edge shows a magnetic transition that is specific to the Ce antiferromagnetic long-range ordering at T Ce ≈ 4 K with short-range Ce ordering above T Ce , whereas neutron diffraction measurements of a few magnetic reflections indicate a transition at T*≈ 12 K with an unusual order parameter. Detailed order-parameter measurements on several magnetic reflections by neutrons show a weak anomaly at 4 K that we associate with the Ce ordering. The successive transitions at T Ce and T* can also be clearly identified by two anomalies in heat capacity and resistivity measurements. The higher transition temperature at T*≈ 12 K is mainly ascribed to Fe spin reorientation transition, below which Fe spins rotate uniformly and gradually in the ab plane. The Fe spin reorientation transition and short-range Ce ordering above T Ce reflect the strong Fe-Ce couplings prior to long-range ordering of the Ce. The evolution of the intricate magnetic structures in CeFeAsO going through T* and T Ce is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Valence, exchange interaction, and location of Mn ions in polycrystalline M n x G a 1 - x N ( x ≤ 0.04 )

In this paper, we present an experimental study for polycrystalline samples of the diluted magnetic semiconductor $\mathrm{M}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1{-}x}\mathrm{N}(x{\le}0.04)$ in order to address some of the existing controversial issues. X-ray and neutron diffraction, x-ray absorption near-edge structure, and electron paramagnetic resonance experiments were used to characterize the structural, electronic, and magnetic properties of the samples, and inelastic neutron scattering was employed to determine the magnetic excitations associated with Mn monomers and dimers. Our main conclusions are as follows: (i) The valence of the Mn ions is $2+$. (ii) The $\mathrm{M}{\mathrm{n}}^{2+}$ ions experience a substantial single-ion axial anisotropy with parameter D = 0.027(3) meV. (iii) Nearest-neighbor $\mathrm{M}{\mathrm{n}}^{2+}$ ions are coupled antiferromagnetically. Finally, the exchange parameter $J={-}0.140(7)\mathrm{meV}$ is independent of the Mn content $x$; i.e., there is no evidence for hole-induced modifications of $J$ towards a potentially high Curie temperature postulated in the literature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

An extended N-H bond, driven by a conserved second-order interaction, orients the flavin N5 orbital in cholesterol oxidase

The protein microenvironment surrounding the flavin cofactor in flavoenzymes is key to the efficiency and diversity of reactions catalysed by this class of enzymes. X-ray diffraction structures of oxidoreductase flavoenzymes have revealed recurrent features which facilitate catalysis, such as a hydrogen bond between a main chain nitrogen atom and the flavin redox center (N5). A neutron diffraction study of cholesterol oxidase has revealed an unusual elongated main chain nitrogen to hydrogen bond distance positioning the hydrogen atom towards the flavin N5 reactive center. Investigation of the structural features which could cause such an unusual occurrence revealed a positively charged lysine side chain, conserved in other flavin mediated oxidoreductases, in a second shell away from the FAD cofactor acting to polarize the peptide bond through interaction with the carbonyl oxygen atom. Double-hybrid density functional theory calculations confirm that this electrostatic arrangement affects the N-H bond length in the region of the flavin reactive center. We propose a novel second-order partial-charge interaction network which enables the correct orientation of the hydride receiving orbital of N5. The implications of these observations for flavin mediated redox chemistry are discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Cryogenic Neutron Protein Crystallography: routine methods and potential benefits

The use of cryocooling in neutron diffraction has been hampered by several technical challenges such as the need for specialized equipment and techniques. Recently we have developed and deployed equipment and strategies that allow for routine neutron data collection on cryocooled crystals using off the shelf components. This system has several advantages, compared to a closed displex cooling system such as fast cooling coupled with easier crystal mounting and centering. The ability to routinely collect cryogenic neutron data for analysis will significantly broaden the range of scientific questions that can be examined by neutron protein crystallography. Cryogenic neutron data collection for macromolecules has recently become available at the new Biological Diffractometer BIODIFF at FRM II and the Macromolecular Diffractometer (MaNDi) at the Spallation Neutron Source, Oak Ridge National Laboratory. To evaluate the benefits of a cryocooled neutron structure we collected a full neutron data set on the BIODIFF instrument on a Toho-1 lactamase structure at 100K.

Weiss, Kevin L.↗