Search NASA⌕ Search

SEARCH · Search NASA

Results for “Neutron Diffraction”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Neutron Residual Stress Mapping of Repaired Spent Nuclear Fuel Welded Stainless-Steel Canisters

Stress corrosion cracking (SCC) caused by atmospheric deposition and deliquescence of aggressive compounds such as chloride-containing salts or oxidized sulfur species may pose a potential issue to the extended service life of spent nuclear fuel (SNF) storage canisters. When a chemically susceptible material is exposed to a hostile environment (e.g., coastal salt air) for a sufficient length of time, SCC may occur at locations on the canister which have undergone high tensile residual stress. These locations are often found in weld zones and the heat-affected zones (HAZ) of welded joints. Ideally, these cracks could be repaired by traditional fusion welding techniques, but the highly localized heat input of the repair welding may introduce additional high tensile residual stress and could increase the risk for future SCCs. This paper presents the results of neutron residual stress mapping of as-welded and repaired stainless steel specimens. The as-welded specimens were provided by Sandia National Laboratories from a canister mock-up manufactured using procedures similar to those used for actual canister production. ASME-qualified gas-tungsten arc welding (GTAW) was used to repair the specimens, and post-repair residual stresses were measured using neutron diffraction at the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR). As-welded and repaired specimen residual stress distributions are evaluated and compared.

Chatzidakis, Stylianos↗
DOE OSTI2020

STRUCTURE AND PROPERTIES STUDY ON ENERGY MATERIALS: THERMOELECTRIC MATERIAL TETRAHEDRITE AND LITHIUM ION CONDUCTOR

Development of efficient energy materials is critical in order to ease the energy demand and reduce our dependence of fossil fuel. Thermoelectric materials are promising due to their capability of generating electrical power by recovering waste heat. The performance of thermoelectric materials is quantified by a dimensionless figure of merit zT, which depends on their properties such as electrical conductivity, Seebeck coefficient and thermal conductivity. Tetrahedrites, a copper antimony sulfosalt mineral, typified by Cu 12-x MxSb 4 S 13 , where M is a transition metal element such as Ni, Zn, Fe or Mn, have great potential for thermoelectric application due to their relatively high zT (close to 1 at 700 K), earth-abundance, environmental friendliness, favorable electrical properties, and most importantly intrinsic low lattice thermal conductivity (less than 1 W m -1 K -1 ) in wide temperature. In addition to energy recovery, reliable energy storage devices are also emerging to relieve the energy demand and improve the efficiency of consuming energy resources. Lithium-ion batteries are known to be reliable and successful electrochemical energy storage devices and appliable in various aspects, including laptops, smartphones and electrical vehicles. Lithium phosphorous oxynitride (LiPON) are widely used as thin-film solid-state electrolytes in Li-ion battery, which is the only demonstrated solid-state electrolyte that is quite stable in direct contact with Li metal at potentials from 0-5 V. However, the structure of LiPON, the effects of N doping, and the origin of its good electrochemical stability remains inconclusive. In this thesis, reliable modeling techniques accompanied with experimental tools, are applied to study the thermoelectric material tetrahedrite and the ionic conductor LiPON, in order to study their structural and dynamical properties. Accurate and efficient density-functional theory (DFT) and density-functional tight-binding (DFTB) methods, combined with molecular dynamics (MD) simulations are utilized in order to investigate the structures and properties of these energy materials. The incoherent and coherent atomic dynamics study of tetrahedrite Cu 10.5 NiZn 0.5 Sb 4 S 13 provides the origin of softening upon cooling by investigate the motion of Cu12e at different temperatures. The dynamic structure factors in the longitudinal and transverse direction will also be discussed. The Cu movement of Cu-rich tetrahedrite Cu 14 Sb 4 S 13 is revealed by Cu self-diffusivity, nuclear density map and “nudged elastic band” (NEB). Moreover, we investigate the effect of simulation cell size and basis sets on the DFT-based MD simulation results using tetrahedrite Cu1 0 Zn 2 Sb 4 S 13 thermoelectric as a model material, showing the advantage of larger cell by accessing smaller Q range. In addition, the low-temperature structural properties of Cu 12 Sb 4 S 13 is measured by neutron diffraction, which indicates that no cubic to tetragonal transition occurs at metal-semiconductor transition (MST) temperature. Thermoelectric properties such as Seebeck coefficient, electrical resistivity and electrical thermal conductivity will also be investigated. DFTB method is implemented to study the structure and transport properties of Li 3 PO 4 and LiPON, while the exploration of N doping effect is included. Lastly, the LiPON/Li interphase will be revealed in order to study the origin of electrochemical stability.

Li, Junchao↗
DOE OSTI2020

STRUCTURE AND PROPERTIES STUDY ON ENERGY MATERIALS: THERMOELECTRIC MATERIAL TETRAHEDRITE AND LITHIUM ION CONDUCTOR LiPON

Development of efficient energy materials is critical in order to ease the energy demand and reduce our dependence of fossil fuel. Thermoelectric materials are promising due to their capability of generating electrical power by recovering waste heat. The performance of thermoelectric materials is quantified by a dimensionless figure of merit zT, which depends on their properties such as electrical conductivity, Seebeck coefficient and thermal conductivity. Tetrahedrites, a copper antimony sulfosalt mineral, typified by Cu12-xMxSb4S13, where M is a transition metal element such as Ni, Zn, Fe or Mn, have great potential for thermoelectric application due to their relatively high zT (close to 1 at 700 K), earth-abundance, environmental friendliness, favorable electrical properties, and most importantly intrinsic low lattice thermal conductivity (less than 1 W m-1 K-1) in wide temperature. In addition to energy recovery, reliable energy storage devices are also emerging to relieve the energy demand and improve the efficiency of consuming energy resources. Lithium-ion batteries are known to be reliable and successful electrochemical energy storage devices and appliable in various aspects, including laptops, smartphones and electrical vehicles. Lithium phosphorous oxynitride (LiPON) are widely used as thin-film solid-state electrolytes in Li-ion battery, which is the only demonstrated solid-state electrolyte that is quite stable in direct contact with Li metal at potentials from 0-5 V. However, the structure of LiPON, the effects of N doping, and the origin of its good electrochemical stability remains inconclusive.In this thesis, reliable modeling techniques accompanied with experimental tools, are applied to study the thermoelectric material tetrahedrite and the ionic conductor LiPON, in order to study their structural and dynamical properties. Accurate and efficient density-functional theory (DFT) and density-functional tight-binding (DFTB) methods, combined with molecular dynamics (MD) simulations are utilized in order to investigate the structures and properties of these energy materials. The incoherent and coherent atomic dynamics study of tetrahedrite Cu10.5NiZn0.5Sb4S13 provides the origin of softening upon cooling by investigate the motion of Cu12e at different temperatures. The dynamic structure factors in the longitudinal and transverse direction will also be discussed. The Cu movement of Cu-rich tetrahedrite Cu14Sb4S13 is revealed by Cu self-diffusivity, nuclear density map and "nudged elastic band" (NEB). Moreover, we investigate the effect of simulation cell size and basis sets on the DFT-based MD simulation results using tetrahedrite Cu10Zn2Sb4S13 thermoelectric as a model material, showing the advantage of larger cell by accessing smaller Q range. In addition, the low-temperature structural properties of Cu12Sb4S13 is measured by neutron diffraction, which indicates that no cubic to tetragonal transition occurs at metal-semiconductor transition (MST) temperature. Thermoelectric properties such as Seebeck coefficient, electrical resistivity and electrical thermal conductivity will also be investigated. DFTB method is implemented to study the structure and transport properties of Li3PO4 and LiPON, while the exploration of N doping effect is included. Lastly, the LiPON/Li interphase will be revealed in order to study the origin of electrochemical stability

25 ENERGY STORAGE↗
DOE OSTI2023

Fundamentals of SrCoO 3-δ Based Oxygen Deficient Perovskites as Cathodes for Solid Oxide Fuel Cells

The local structure and oxygen stoichiometry in oxide systems have a profound impact on oxygen electrocatalysis encountered in metal-air batteries and solid oxide fuel cells (SOFCs). However, this knowledge is often obtained under conditions different from the real working conditions of the material, resulting in misinterpretation and misunderstanding. This PhD dissertation aims to obtain the structure and oxygen-stoichiometry information of a class of perovskite oxides under their real working conditions in solid oxide fuel cells. Several perovskite oxides were selected for the study: Sr 0.9 Y 0.1 CoO 3-δ (SYC10), Sr 0.9 Y 0.3 CoO 3-δ (SYC30), SrCo 0.9 Nb 0.1 O 3-δ (SCN10) and SrCo 0.9 Ta0.1O 3-δ (SCT10). The local crystal structure and oxygen stoichiometry of these materials were systematically characterized with in-situ neutron diffraction (ND). The oxygen stoichiometry was also measured by thermogravimetric analysis (TGA) and iodometric titration methods. To establish the correlation among structure, oxygen stoichiometry and oxygen reduction reaction (ORR) activity, high temperature electrochemical impedance spectroscopy, oxygen permeation and single cell testing were also performed. In chapter 2, SYC10 is described to have a more symmetrical structure and $V_o^{··}$ distribution, and higher $V_o^{··}$ concentration than SYC30. Molecular orbital energy analysis based on the local structure of the ORR-active Co1-polyhedra indicates SYC30 has a higher Fermi level relative to O-2p energy level in the active Co1-polyhedra, and thus a higher motional enthalpy for $V_o^{··}$ migration. However, the ORR activity of Y-doped SrCoO 3-δ (SCO) are found uncompetitive with other popular catalysts. In chapter 3 and 4, systematic structural studies are presented for Nb and Ta-doped SCO, namely SCN10 and SCT10, respectively. The methodology of unrevealing the structure-activity relationships in chapter 2 is also found applicable to SYC10, SCN10 and SCT10 as presented in chapter 5. The electrochemical tests indicate that SCT10 is the best catalyst due to its excellent thermal and electrochemical stability. In chapter 6, SCT10 is evaluated in a real solid oxide fuel cell in the form of nanoscaled SCT10 layer coating on the commercial (La 0.6 Sr 0.4 ) 0.95 Co 0.2 Fe 0.8 O 3-δ (LSCF). The bilayer structured cathode shows excellent properties of coarsening-resistant, Sr-segregation-free and high ORR-activity.

Yang, Tianrang↗
DOE OSTI2016

A Comparison of Modeling Strategies for Additively Manufactured HFIR Control Elements

The High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory is a flux-trap type research reactor that is used for a range of research applications, including neutron scattering experiments, materials irradiation tests, and isotope production. The HFIR core comprises several concentric cylindrical regions; starting from the core centerline and moving radially outwards, these are the flux trap target (FTT) region, the inner and outer fuel elements (IFE and OFE), the inner and outer control elements (ICE and OCE), and the reflector region. The control elements (CEs) are axially zoned into regions of differing absorption strength: the white regions contain only structural aluminum and do not significantly contribute to reactivity control; the gray regions contain tantalum as the primary absorber with a concentration of 38% by volume, and the black regions contain europia (Eu{sub 2}O{sub 3}) as the primary absorber with a concentration of 31% by volume. During operation, the CEs are withdrawn symmetrically in opposite directions from the core to remove the neutron absorbers from the core and maintain criticality. The current approach to fabrication of the HFIR CEs is tedious, outdated, and expensive. In an effort to improve the operational economics of HFIR and to demonstrate the feasibility of advanced manufacturing techniques for production of nuclear reactor components, novel methods for production of neutron-poison bearing aluminum structures have been initiated at ORNL. For this application, the ultrasonic additive manufacturing (UAM) process involves the use of 3D printing technology to construct small cylindrical compacts (0.559 cm in diameter and 0.171 cm in height) of aluminum mixed with neutron-absorbing material. The compacts contain 60% poison (Ta or Eu{sub 2}O{sub 3}) by volume. These compacts are then embedded into an aluminum matrix before formation into the cylindrical shape appropriate for use in HFIR. The CEs produced in this process therefore contain discrete regions of absorbing material, in contrast to the traditional design with homogeneously distributed absorbers. It is therefore of interest to investigate how the HFIR core behavior with discrete CEs differs from the case with homogeneous CEs with respect to some key reactor physics parameters. The primary objective of this study is to compare modeling strategies for the discrete CE design and examine differences in the core physics between the discrete and homogeneous CE designs as predicted by each model. Lessons learned from this investigation may then be used to inform the design process in future endeavors. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Statistical Study of Primary Knock-on Atoms under Neutron Irradiation in RMC Code

Materials in high flux neutron condition will suffer from an evolution of damage which ultimately restricts the lifetime of the fuel clad and reactor pressure vessel. Atoms in irradiated material transform to primary knock-on atoms (PKAs) by absorbing the kinetic energy transferred from neutrons, and the energy released from nuclear reactions. The secondary collision cascades which are induced by PKAs create point defects within the material, with residual vacancies and interstitials eventually causing swelling and embrittlement that degrades mechanical behavior. For a long time, Displacements per Atom (DPA) index has been identified as a measure of radiation damage in material. Nowadays, several advanced methods, such as Molecular Dynamics (MD) and Kinetic Monte Carlo (KMC) simulations, have been developed for more accurately simulating the evolution of the damage. However, all of these techniques need more comprehensive information of PKA, such as the type, energy, direction and spatial distribution. The limitations of DPA emerge and a method should be provided to simulate the generative process of PKAs. Recently, a deterministic analysis code SPECTRA-PKA has been developed by Gilbert to calculate the energy spectra of almost all types PKAs by solving the group-to-group cross-section matrices equation which includes neutron scattering, light charged particles, and recoils of the residual nuclei. But this deterministic analysis code could not give the direction, spatial and time distribution of PKAs. Based on the Geant4 program, Cui Zhenguo has simulated the irradiation by neutrons with 1 MeV energy in zirconium, while only the two adjacent elastic collisions between injected neutron and target atoms are taken into consideration. In this paper, Monte Carlo method to calculate PKAs information during neutron transport in RMC code is introduced. RMC is a continuous-energy Reactor Monte Carlo neutron and photon transport code being developed by Department of Engineering Physics at Tsinghua University, Beijing. PKAs in zirconium are calculated in fixed neutron source mode. Statistical information of PKAs in PWR fuel cell and SFR fuel cell is shown and compared. The results show that Monte Carlo method can provide more comprehensive information of PKAs. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Development of an In-Beam Neutron Flux Monitor for Time of Flight Capture Measurements

Accurate nuclear data are important in several aspects of nuclear engineering, such as reactor simulations, nonproliferation, and criticality safety. One of the nuclear data measurements that requires reduced uncertainties in its related cross-sections is neutron capture. The neutron capture cross-sections have particular deficiencies in the incident neutron energy range from 1 keV to 1 MeV. This is due to the predominance of scattering reactions in this energy region. In order to provide more accurate measurements in this energy region, a new experimental setup has been designed and created at Rensselaer Polytechnic Institute (RPI). This experiment utilizes several C{sub 6}D{sub 6} detectors in a low mass system to minimize the effects of neutron scattering on the experiment. In order to determine the capture yield for the measurements, several additional factors need to be known about the neutron beam including the energy dependence of the neutron flux incident on the sample. A detector made from a thin piece of EJ-204 plastic scintillator was designed to measure the neutron flux, as a function of incident neutron energy, during the capture measurements. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Quasi-differential neutron induced neutron emission reaction measurements at WNR

The quasi-differential neutron induced neutron emission reaction measurement (QD-NINE) method provides an additional benchmark which constrains cross-section evaluations and provides a measure of verification for existing evaluations. Experiments are preformed using an array of EJ-309 liquid scintillators at a variety of angles measuring the neutron scattering response from a sample.. An MCNP simulation is then compared to this experimental data and is run using various sets of evaluated nuclear data. Since the isotopes of interest for this measurement, {sup 235}U and {sup 239}Pu, are difficult to obtain, the WNR facility at LANL was chosen to perform the measurements utilizing the chi-nu detector array. A measurement of carbon has been performed and the high energy cutoff has been extended from 20 to 60 MeV compared with previous measurements using this method. An early stage simulation was compared to the experimental data and the results show good agreement. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

Ab initio generation of thermal neutron scattering law for uranium dioxide

Neutronic analysis of moderated nuclear fission systems, e.g. nuclear reactors, relies upon an accurate prediction of the thermal neutron spectrum. Thermal neutrons have wavelengths on the order of the interatomic spacing between atoms in matter. Consequently, the scattering cross-sections of these neutrons are affected by the scattering law of the material (i.e. S(α,β), where α and β are dimensionless momentum and energy transfer variables), which describes the atomic structure and thermodynamic motion of the atomic nuclei. Uranium-dioxide (UO{sub 2}) is the primary fuel source for nuclear power reactors moderated by light water. In such systems (e.g. nuclear power reactors, spent fuel pools, etc.) the nuclear fuel comprises a large fraction of the system volume, approximately 1/3 in light-water reactors. Therefore, the scattering law of the fuel material may impact the thermal neutron spectrum and criticality of these systems. In this work previously established ab initio lattice dynamics (AILD) methods were utilized to calculate the phonon density of states (DOS), which acts as a fundamental input to the scattering law. Subsequently, the S(α,β) of UO{sub 2} was generated for publication as an ENDF thermal scattering library (TSL), which will be available for use in standard neutronics computer applications. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2017

Radiological Shielding Design for the Neutron Backscattering Spectrometer EMU

In this paper we present modelling and design of compact radiation shielding required for operation of the EMU instrument, located at Australia's OPAL nuclear reactor. The acceptance criteria for the shielding design were (i) safety - dose rate ≤ 3 μSv/h at external surfaces of the instrument's experimental area, (ii) floor load limit < 20 tons/m{sup 2}, (iii) low cost and (iv) for maintenance purposes 'easy access' to components of the instruments. The EMU instrument is a cold neutron backscattering spectrometer designed to measure inelastic neutron scattering. Its distinctive feature is that it has a tight elastic energy transfer resolution, of about 1 μeV. The instrument provides unique opportunities to study diffusion in complex materials, e.g. water molecules in confinement, polymers or biological molecules, particularly in the Asia-Oceania region. EMU is the first instrument located on the CG3 neutron beam line of the OPAL Neutron Guide Hall (NGH). A pre-existing evacuated neutron guide of dimensions 200 mm (height) x 50 mm (width) feeds into the shared EMU/KOOKABURRA pre-monochromator bunker shielding assembly, and its bottom cross section will be intercepted ∼200 mm further in air by the highly orientated pyrolytic graphite (HOPG) EMU pre-monochromator (take-off angles from 125.4 deg. to 148 deg.). The bunker shielding assembly for EMU also contains a beryllium filter and Focusing Guide Section D (FGD, 170 mm (height) x 50 mm (width)). To accommodate the range of take-off angles Pb cylindrical shielding blocks of radius 140 mm and 500 mm height have been designed. These blocks will be located at the section of the bunker where the neutron beam will exit towards the experimental area and they will reside on top of a hollow steel base (sides 10 mm thick), on which they move by sliding and are integrated with the tertiary shutter. The experimental area is enclosed by a concrete wall of 2.5 m height and 300 mm thickness, shared with the KOOKABURRA instrument, Gyprock Plasterboard panels with viewing windows, a wall from the Out-of-Pile Bunker and the CG3 shielding. The neutron beam enters the experimental area via the tertiary shutter, into the Focusing Guide Section C (FGC), which has an entrance guide cross-section of 158 mm (height) x 79 mm (width) and exit guide cross-section of 149 mm (height) x 85 mm (width) and is of length 816 mm. The vacuum chamber of FGC will be connected to the vacuum chamber of the Background Chopper (BC, disc of outer radius 350 mm). Focusing Guide Section B (FGB) is aligned with FGC and its vacuum shared with the BC vacuum. The FGB has an exit guide cross section of 50 mm (height) x 49 mm (width) and is of length 4046 mm, which will focus the neutron beam vertically and horizontally towards the Al window entrance (0.82 mm thickness, labelled N16) of the Scattering Tank assembly (constructed from 20 mm - 40 mm thickness stainless steel and will be under vacuum < 1 x 10{sup -3} mbar). Inside the Scattering Tank there is another section of Focusing Guide (FGA), with an exit guide cross-section of 30 mm (height) 30 mm (width) and of length 417 mm. The neutron beam exiting the FGA will be reflected by the HOPG crystal pieces of the Graphite Chopper (GC) towards the Backscattering Monochromator (BM). The reflected neutron beam will first pass through the other Al window (0.82 mm thickness, labelled N17) of the Scattering Tank and then enter into a flight tube (steel of 10 mm thickness). The BM is formed in an 1800 mm spherical radius array of Si crystal elements (0.87 mm thickness) and is oscillated by the linear motor Doppler Drive. The neutron beam will be reflected back at 180 deg. from, and focussed by the BM to reenter the Scattering Tank through the N17 Al window. It will then pass through the GC (HOPG crystals are rotated out of the way) and will reach the scattering sample of interest to the instrument end user. Also, inside the Scattering Tank there will be {sup 3}He linear position-sensitive detectors, and Analyser Arrays formed in an 1800 mm radius spherical arrays of Si crystal elements (0.87 mm thickness) glued on aluminium support frames (10 mm thickness) and span ∼160 deg. arc.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2018

Benchmarking of the MCNPX predictions of the neutron time-emission spectra at LANSCE - 25332

We currently operate Mark-III generation of the spallation neutron target-moderator-reflector-shield (TMRS) assembly at the Manuel Lujan Jr. Neutron Scattering Center of the Los Alamos Neutron Science Center (LANSCE). Mark-III is scheduled for replacement with the next-generation TMRS Mark-IV in 2020. Mark-IV enhances the neutronic performance in the eV-MeV energy range by increasing intensity and improving energy resolution. The increased eV-MeV neutron flux, together with the elevated gamma-ray background, has implications for the radiation shielding of the neutron flight paths and scientific instruments. To update the shielding design, we need to maintain a thoroughly benchmarked MCNPX model of the entire TMRS assembly. In this article we use our detailed MCNPX model of Mark-III to calculate the neutron time-emission spectra. With these spectra we generate the resolution function for SAMMY calculations of capture cross section in {sup 197}Au in the resonance region between 70 eV and 1 keV. We compare the calculated data with the experimental data measured with the DANCE instrument using the neutron time-of-flight technique. We show that our current model predicts measurements accurately and thus provides a solid base for developing the radiation shielding design of the new TMRS assembly. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2018

Shielding maze design for Line C tunnel at LANSCE - 25456

The Los Alamos Neutron Science Center (LANSCE) is a major experimental facility at Los Alamos National Laboratory. The LANSCE linear accelerator (linac) supplies proton beams to five experimental areas simultaneously. The Isotope Production Facility (IPF) utilizes a 100-MeV beam after the first stage of acceleration, all other facilities use proton beams at 800 MeV. However, the facility can support sole-use experiments at 200-600 MeV proton beam energies. There are three spallation neutron sources providing neutrons in different energy regimes: Weapons Neutron Research (WNR), Lujan Neutron Scattering Center (Lujan Center) and the Ultra Cold Neutron source (UCN). The proton radiography (pRAD) facility utilizes the energetic proton beam for imaging and tomography directly. The beam to pRAD and UCN facilities is delivered via line X that splits into line C (pRAD) and line B (UCN). Due to engineering access controls it is impossible to deliver beam to UCN while the pRAD facility is occupied. The goal of our project was to design a shielding maze arrangement for line C to allow for simultaneous beam delivery to UCN while pRAD area (dome) is occupied. (authors)

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

ENDF/B-VIII.0: the 8. major release of the ENDF/B library containing CIELO-project evaluations, new standards and thermal scattering data - 25580

The ENDF/B-VIII.0 evaluated nuclear reaction data library was released on February 2, 2018. ENDF/B-VIII.0 incorporates many improvements including the new IAEA standards, a nearly completely new thermal neutron scattering sublibrary and the CIELO project evaluations for neutron reactions on {sup 16}O, {sup 56}Fe, {sup 235}U, {sup 238}U and {sup 239}Pu. These evaluations are a direct result of improvements in theory and simulation and benefit from recent experimental data obtained in the U.S. and Europe. Notable other advances include updated evaluated data for light nuclei, structural materials, actinides and charged-particle reactions, and specific updates to fission energy release, prompt fission neutron and γ-ray spectra. ENDF/B-VIII.0 has undergone substantial testing including a wide range of criticality, reaction rate, and shielding benchmarks. Our integral validation demonstrates that performance of the library is a noticeable improvement over the previous ENDF/B-VII.1 library. (authors)

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

A suite-level review of the neutron single-crystal diffraction instruments at Oak Ridge National Laboratory

The nascent suite of single-crystal neutron diffractometers at the Oak Ridge National Laboratory has no equal at any other neutron scattering facility worldwide and offers the potential to re-assert single-crystal diffraction using neutrons as a significant tool to study nuclear and magnetic structures of small unit cell crystals, nuclear structures of macromolecules, and diffuse scattering. Signature applications and features of single-crystal neutron diffraction are high resolution nuclear structure analysis, magnetic structure and spin density determinations, contrast variation (particularly D 2 O/H 2 O) for nuclear structural studies, lack of radiation damage when using crystals of biological molecules such as proteins, and the fidelity to measure nuclear and magnetic diffuse scattering with elastic discrimination.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Effect of Collimation on Diffraction Signal-to-Background Ratios at a Neutron Diffractometer

High diffraction signal-to-background ratios (SBRs), the ratios of diffraction peak integrated intensity over its background intensity, are desired for a neutron diffractometer to acquire good statistics for diffraction pattern measurements and subsequent data analysis. For a given detector, while the diffraction peak signals primarily depend on the characteristics of neutron beam and sample coherent scattering, the background largely originates from the sample incoherent scattering and the scattering from the instrument space. In this work, we investigated the effect of collimation on neutron diffraction SBRs of Si powder measurements using one high-angle area detector bank coupled with six different collimation configurations in a large and complex instrument space at the engineering materials diffractometer VULCAN, SNS, ORNL. The results revealed that the diffraction SBRs can be significantly improved by a proper coarse collimator that leaves no gap between the detector and the collimator, and the improvement of SBRs by a fine radial collimator was remarkable with a proper coarse collimator in place but not distinguishable without one. It was also found that the diffraction SBRs were not effectively improved by adding neutron absorbing element boron to the fine radial collimator body, which indicates that either the absorption of secondary scattered neutrons by the added boron is insignificant or the collimator base material (resin and ABS) alone attenuates background scattering sufficiently. These findings could serve as a useful reference for diffractometer developers and/or operators to optimize their collimation to achieve higher diffraction SBRs.

Yu, Dunji↗
DOE OSTI2025

Localized triplons and site stuffing in the quantum dimer magnet BiYbGeO5

Thermodynamic and muon spin relaxation measurements have recently highlighted BiYbGeO5 as a new example of a rare-earth-based quantum dimer magnet with isolated Yb3+ spin-1/2 dimers. However, direct spectroscopic evidence of the triplet excitations and measurements of the structural disorder are lacking. In this work, polycrystalline BiYbGeO5 was synthesized using conventional high-temperature solid-state methods and investigated via high-resolution neutron powder diffraction and inelastic neutron scattering. Diffraction measurements down to 58 mK reveal no signatures of magnetic order and indicate that nearly 20% of Yb3+ sites are replaced by nonmagnetic Bi3+, introducing significant structural disorder. Inelastic neutron scattering shows dispersionless triplon excitations, consistent with localized, noninteracting spin dimers. Fits to the triplet excitation spectrum with an XXZ-type anisotropic exchange give 𝐽XX=0.100⁢(1)⁢meV and 𝐽Z=0.202⁢(1)⁢meV. These findings establish BiYbGeO5 as a structurally disordered but magnetically well-isolated quantum dimer system, providing a model platform for studying the resilience of entangled spin states to site dilution.

Kapoor, Rachit [Brock University, Canada]↗
DOE OSTI2018

Crystal Structure and Coordination of B-Cations in the Ruddlesden–Popper Phases Sr3−xPrx(Fe1.25Ni0.75)O7−δ (0 ≤ x ≤ 0.4)

Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mössbauer spectroscopy. Both samples, prepared at 1300 °C under N2(g) flow and samples subsequently air-annealed at 900 °C, were studied. The structures contained oxygen vacancies in the perovskite layers, and the Fe/Ni cations had an average coordination number less than six. The oxygen content was considerably higher for air-annealed samples than for samples prepared under N2, 7 − δ = ~6.6 and ~5.6 per formula unit, respectively. Mössbauer data collected at 7 K, below magnetic ordering temperatures, were consistent with X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) results. The electrical conductivity was considerably higher for the air-annealed samples and was for x = 0.1~30 S·cm−1 at 500 °C. The thermal expansion coefficients were measured in air between room temperature and 900 °C and was found to be 20–24 ppm·K−1 overall.

36 MATERIALS SCIENCE↗