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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.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Learning continuous scattering length density profiles from neutron reflectivities using convolutional neural networks

Interpreting neutron reflectivity (NR) data using ad hoc multi-layer models and physics-based models provides information about spatially resolved neutron scattering length density (NSLD) profiles. Recent improvements in data acquisition systems have allowed acquiring thousands of NR curves in a couple of hours, which has led to a need for automated data analysis tools to interpret NR measurements in real-time. Here, we present a machine learning analysis workflow that uses a series of models, based on a convolutional neural network (CNN), to learn the relation between the NSLDs and the NRs, and subsequently produce continuous NSLD profiles directly from NRs. The usefulness of our CNN-based models is demonstrated by constructing NSLDs from NRs of several films containing homopolymer polyzwitterions and diblock copolymers mixed with different types of salts. Comparisons of the NSLDs with those constructed using ad hoc multi-layer models reveal a very good agreement, suggesting the potential of CNN-based models for real-time automated data analysis of NRs.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Neutron Reflectometry Reveals Diffusion in Contrast-Matched Brush Particle Bilayers

A material system for performing layer-spread experiments on brush particle bilayers is presented and used to determine the diffusion constant of brush particles in the melt state. Selective deuteration of the core and shell of organo-silica nanoparticles grafted with poly(methyl methacrylate) was used to match the scattering length density of the core and the polymer canopy layer. This subdued the scattering of particle cores (i.e., formfactor scattering) and enabled the analysis of the interdiffusion kinetics using neutron reflectivity. For low molecular grafts, i.e., grafts with a molecular weight below the entanglement limit, the interdiffusion kinetics revealed both a sub- and Fickian diffusion regime. The former was attributed to the local dynamics that was constrained by the slow-moving cores of neighboring brush particles that acted as long-lived physical cross-links. No transition to Fickian diffusion was observed for entangled systems, even at prolonged annealing times. This suggested a higher level of kinetic restraint in entangled brush particle melts as compared to, for example, star polymers with a comparable chain length for which Fickian diffusion has been reported under similar conditions.

Diffusion, Polymer Grafted Nanoparticles, Neutron ↗
DOE OSTI2025

Applications of quantum materials in nuclear physics experiments (Final Report)

The goals of this project are to search for hypothesized spin-hall effects of neutrons and variants of neutron-electron hybrid spin hall effects in quantum materials with strong spin-orbit-coupling (SOC) – such as: • Deflection of neutrons dependent on spin (polarization) states (a); • Electrical current induced electron spin polarization or (dynamically polarized) nuclear spin polarization (as suggested in PI’s prior work) may affect polarization states of transmitted or reflected neutron beam • Spin polarized neutrons transfer some spin angular momenta to electrons, which get converted to electronic charge voltage via electronic inverse spin Hall effect (b), which if realized, offers an electrical method to detect neutron spins.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Confined Room-Temperature Ferromagnetism in Kagome (Fe 3 Sn 2 /CoSn) Superlattices

We reveal the presence of robust ferromagnetism in topological kagome (Fe 3 Sn 2 /CoSn) ×n superlattices via polarized neutron reflectivity (PNR) and magnetization measurements. Using molecular beam epitaxy, we have synthesized superlattices of alternating ferromagnetic Fe 3 Sn 2 and paramagnetic CoSn layers, the interfacial integrity of which is confirmed using scanning transmission electron microscopy. Magnetization depth profiles, obtained by fitting the PNR data, confirm the presence of ferromagnetism in the confined Fe 3 Sn 2 layers at room temperature, with minimal thickness dependence down to 2 nm. A net magnetization is found in the near-surface region of CoSn, which we attribute to surface oxidation. Our results demonstrate that superlattice engineering is a means to confine ferromagnetism in kagome metals, enabling future studies of thickness-dependent anomalous Hall and Nernst effects as well as spin-dependent transport and tunneling in device structures.

kagome metals↗
DOE OSTI2025

Role of Salt Concentration on Interphase Dynamics and Chemistry of Silicon Anodes during Electrochemical Cycling

We investigated the chemistry and structure of the solid electrolyte interphase (SEI) grown over a silicon anode as a function of the lithium salt concentration. In these experiments, in situ neutron reflectivity measurements were performed to measure the thickness and composition of the SEI formed from 1.0 and 5.5 M lithium bis(trifluoromethane)sulfonimide (LiTFSI) in standard ethylene carbonate:dimethyl carbonate electrolytes. These measurements reveal the formation of a 350+ Å thick SEI layer that is predominantly organic (∼80%) and dimensionally stable when using a 1.0 M salt solution. In contrast, increasing the salt concentration to 5.5 M resulted in an SEI that exhibited thickness changes from 100 to 375 Å and became up to 30% inorganic. In conclusion, these compositional and structural changes point to the role of salt speciation on the resulting passivation of silicon electrodes and indicate the need to form more organic-like passivation layers to promote the calendar life of silicon anodes.

Electrodes↗
DOE OSTI2026

Neutron skins probed in proton knockout from neutron-rich nuclei

Proton-induced quasifree knockout reactions provide a powerful probe of nuclear single-particle structure and reaction dynamics in both stable and neutron-rich nuclei. Here, in this work, we develop a unified theoretical framework for the calculation of inclusive (𝑝, 2⁢𝑝) and sequential (𝑝, 3⁢𝑝) reaction cross sections and fragment momentum distributions at intermediate and relativistic energies. The approach is based on a probabilistic extension of Glauber multiple-scattering theory combined with microscopic nuclear densities obtained from Hartree-Fock-Bogoliubov calculations using Skyrme energy-density functionals. We focus in particular on the sensitivity of total cross sections and longitudinal momentum dispersions to neutron-skin thickness along isotopic chains. Our results indicate that both (𝑝, 2⁢𝑝) and (𝑝, 3⁢𝑝) reactions exhibit a systematic decrease of cross section and momentum width with increasing neutron excess, reflecting enhanced attenuation and surface bias induced by neutron skins. The effect is significantly stronger for two-proton removal, suggesting that (𝑝, 3⁢𝑝) reactions may offer enhanced sensitivity to isovector nuclear structure. These findings establish proton-induced knockout reactions as complementary hadronic probes of neutron skins and the density dependence of the nuclear symmetry energy.

direct reactions↗
NASA NTRS2018

Detection of Reflection Features in the Neutron Star Low-mass X-Ray Binary Serpens X-1 with NICER

We present Neutron Star Interior Composition Explorer (NICER) observations of the neutron star (NS) low-mass X-ray binary Serpens X-1 during the early mission phase in 2017. With the high spectral sensitivity and low-energy X-ray passband of NICER, we are able to detect the Fe L line complex in addition to the signature broad, asymmetric Fe K line. We confirm the presence of these lines by comparing the NICER data to archival observations with XMM-Newton/Reflection Grating Spectrometer (RGS) and NuSTAR. Both features originate close to the innermost stable circular orbit (ISCO). When modeling the lines with the relativistic line model RELLINE, we find that the Fe L blend requires an inner disk radius of 1.4(sup 0.2, sub -0.1)R(sub ISCO) and Fe K is at 1.03(sup 0.13, sub -0.03)R(sub ISCO) (errors quoted at 90%). This corresponds to a position of 17(sup 2.5, sub -1.2)km and 12(sup 1.6, sub -0.4)km for a canonical NS mass (M(sub NS)=1.4 solar mass) and dimensionless spin value of a = 0. Additionally, we employ a new version of the RELXILL model tailored for NS(sub s) and determine that these features arise from a dense disk and supersolar Fe abundance.

Ludlam, R. M.↗
DOE OSTI2024

Microstructural Underpinnings of Giant Intrinsic Exchange Bias in Epitaxial NiCo 2 O 4 Thin Films

Understanding intrinsic exchange bias in nominally single-component ferromagnetic or ferrimagnetic materials is crucial for simplifying related device architectures. However, the mechanisms behind this phenomenon and its tunability remain elusive, which hinders the efforts to achieve unidirectional magnetization for widespread applications. Inspired by the high tunability of ferrimagnetic inverse spinel NiCo 2 O 4 , the origin of intrinsic exchange bias in NiCo 2 O 4 (111) films deposited on Al 2 O 3 (0001) substrates are investigated. The comprehensive characterizations, including electron diffraction, X-ray reflectometry and spectroscopy, and polarized neutron reflectometry, reveal that intrinsic exchange bias in NiCo 2 O 4 (111)/Al 2 O 3 (0001) arises from a reconstructed antiferromagnetic rock-salt Ni x Co 1-x O layer at the interface between the film and the substrate due to a significant structural mismatch. Remarkably, by engineering the interfacial structure under optimal growth conditions, it can achieve exchange bias larger than coercivity, leading to unidirectional magnetization. Such giant intrinsic exchange bias can be utilized for realistic device applications. This work establishes a new material platform based on NiCo 2 O 4 , an emergent spintronics material, to study tunable interfacial magnetic and spintronic properties.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Chromium isotopic anomalies in the Allende meteorite

Abundances of the chromium isotopes in terrestrial and bulk meteorite samples are identical to 0.01 percent. However, Ca-Al-rich inclusions from the Allende meteorite show endemic isotopic anomalies in chromium which require at least three nucleosynthetic components. Large anomalies at Cr-54 in a special class of inclusions are correlated with large anomalies at Ca-48 and Ti-50 and provide strong support for a component reflecting neutron-rich nucleosynthesis at nuclear statistical equilibrium. This correlation suggests that materials from very near the core of an exploding massive star may be injected into the interstellar medium.

Papanastassiou, D. A.↗
NASA NTRS2010

Wolter Optics for Neutron Focusing

Focusing optics based on Wolter optical geometries developed for x-ray grazing incidence beams can be designed for neutron beams. Wolter optics are formed by grazing incidence reflections from two concentric conic sections (for example, a paraboloid and a hyperboloid). This has transformed observational X-ray astronomy by increasing the sensitivity by many orders of magnitude for research in astrophysics and cosmology. To increase the collection area, many reflecting mirrors of different diameters are nested with a common focal plane. These mirrors are fabricated using nickel-electroformed replication techniques. We apply these ideas to neutron focusing using nickel mirrors. We show an initial test of a conical mirror using a beam of cold neutrons. key words: electroformed nickel replication, focusing optics, grazing angle incidence, mirror reflection, neutron focusing, Wolter optics

Mildner, D. F. R.↗
NASA NTRS2012

Development of Grazing Incidence Optics for Neutron Imaging and Scattering

Because of their wave nature, thermal and cold neutrons can be reflected from smooth surfaces at grazing incidence angles, be reflected by multilayer coatings or be refracted at boundaries of different materials. The optical properties of materials are characterized by their refractive indices which are slightly less than unity for most elements and their isotopes in the case of cold and thermal neutrons as well as for x-rays. The motivation for the optics use for neutrons as well as for x-rays is to increase the signal rate and, by virtue of the optic's angular resolution, to improve the signal-to-noise level by reducing the background so the efficiency of the existing neutron sources use can be significantly enhanced. Both refractive and reflective optical techniques developed for x-ray applications can be applied to focus neutron beams. Typically neutron sources have lower brilliance compared to conventional x-ray sources so in order to increase the beam throughput the neutron optics has to be capable of capturing large solid angles. Because of this, the replicated optics techniques developed for x-ray astronomy applications would be a perfect match for neutron applications, so the electroformed nickel optics under development at the Marshall Space Flight Center (MSFC) can be applied to focus neutron beams. In this technique, nickel mirror shells are electroformed onto a figured and superpolished nickel-plated aluminum cylindrical mandrel from which they are later released by differential thermal contraction. Cylindrical mirrors with different diameters, but the same focal length, can be nested together to increase the system throughput. The throughput can be increased further with the use of the multilayer coatings deposited on the reflectivr surface of the mirror shells. While the electroformed nickel replication technique needs to be adopted for neutron focusing, the technology to coat the inside of cylindrical mirrors with neutron multilayers has to be developed. The availability of these technologies would bring new capabilities to neutron instrumentation and, hence, lead to new scientific breakthroughs. We have established a program to adopt the electroformed nickel replication optics technique for neutron applications and to develop the neutron multilayer replication technology.

Gubarev, M. V.↗
DOE OSTI2025

Multi-cycle reload analysis of a long cycle gas-cooled fast modular reactor

There is currently significant interest in deploying HALEU-fueled fast reactors, including the General Atomics (GA) Fast Modular Reactor (FMR). Such reactors can achieve very long fuel cycles, but with multi-batch loading will take decades to reach equilibrium. This motivates design and analysis of both the initial core and multi-cycle reload, which is typically performed using fast-running, deterministic fast reactor codes such as the Argonne Reactor Computation (ARC) codes. In this paper, multicycle reload of the GA FMR is analyzed using the ARC codes. The GA FMR utilizes 19.75 % enriched fuel in a 16 year cycle with a three-batch strategy, with twice-burned fuel placed on the core periphery. The GA FMR has a softened neutron spectrum due to reflecting elements in the core, so the neutronic solution is first benchmarked against the OpenMC Monte Carlo code. Discrepancy on k eff is 400–600 pcm, likely due to the softened neutron spectrum, heterogeneous fuel assembly design and central reflector. However, the rms discrepancy on the assembly power distribution is only 0.6 %, despite the presence of the central reflector. A reload strategy is devised for the first three cycles of such a reactor, ultimately spanning the first 45–48 years of its operation. The fresh core uses 19.75 %, 19.25 % and 16.75 % enriched fuel in place of fresh, once-burned and twice-burned and is then subsequently refueled with only 19.75 % enriched fuel. The cycle length is varied over 3 cycles of operation to balance fuel utilization and reactor availability, specifically with use of an extended 18-year Cycle 1, followed by a shortened 11-year Cycle 2. Cycle 3 is close to the target 16-year length. Finally, placing twice burned assemblies next to the GA FMR central reflector can reduce power peaking by 3 %, at the expense of slightly reducing the cycle length.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2011

From X-Ray Telescopes to Neutron Focusing

In the case of neutrons the refractive index is slightly less than unity for most elements and their isotopes. Consequently, thermal and cold neutrons can be reflected from smooth surfaces at grazing-incidence angles. Hence, the optical technologies developed for x-ray astronomy can be applied for neutron focusing. The focusing capabilities of grazing incidence neutron imaging optics have been successfully demonstrated using nickel mirrors. The mirrors were fabricated using an electroformed nickel replication process at Marshall Space Flight Center. Results of the neutron optics experiments will be presented. Challenges of the neutron imaging optics as well as possible applications of the optics will be discussed.

Gubarev, M. V.↗
DOE OSTI2025

Physical and thermal property changes under uniform oxidation in nuclear graphite

Material property changes of fine- and medium-grain nuclear graphite grades were measured after subjection to uniform oxidation. The cores of high temperature reactors are composed of large nuclear graphite block components. Here, these large core components are designed to provide neutron moderation and reflection, create a large thermal sink to assist in operational control, and form the solid core structure containing the nuclear fuel, coolant channels, and the safety critical channels for control rod insertion. Oxidation is a principle degradation mechanism affecting all aspects of the nuclear graphite component functions. This study addresses the underlying physical property changes of nuclear-graphite components for oxidized mass loss ranges beyond the current recommended ASME code rule limits to ensure structural integrity within the graphite components (a maximum mass loss = 10%).

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Alternative Method for Performing As-Built, As-Irradiated Neutronics Analyses

Neutronics analyses have been used to assist in the design, development, and qualification of miniature fuel (MiniFuel) experiments irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) since their conception almost a decade ago. In recent years, upon completion of a MiniFuel target’s irradiation, neutronics analyses that reflect the as-built, as-irradiated conditions of an experiment have also been performed to validate postirradiation examination (PIE) efforts. Several radiation transport and depletion/activation software wrapper programs have been developed to increase the fidelity of these calculations; at ORNL, a program called HFIRCON is the primary software method employed. However, the utilization of these wrapper programs comes at a cost. To produce accurate results, the radiation transport portion of these analyses requires significant time and resources to execute. Therefore, this report discusses an alternative methodology for calculating some of the desired output for PIE validation—specifically, the output used in evaluating the experiment’s fuel burnup—without complete reliance on ORNL’s wrapper program. The alternative method is not a new software but rather a procedure for utilizing the depletion/activation software, SCALE, in conjunction with limited input data and reasonable assumptions to bypass most of the radiation transport calculations and thereby reduce the time required for the completion of a standard analysis.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1971

Neutron capture on Sm-149 in lunar samples.

High precision isotopic composition measurements of Sm have been carried out for two terrestrial and seven lunar samples from three Apollo sites. The lunar samples, selected to show a wide variation in cosmic ray exposure ages, have a wide range of enrichments in Sm-150/Sm-154 (up to 0.8%) and depletions in Sm-149/Sm-154 which are due to neutron capture. The ratio of the number of neutrons captured per atom by Sm-149 to Gd-157 is 0.9 and reflects a hardened lunar neutron spectrum. This ratio is in reasonable but not exact agreement with that obtained from the theoretical lunar neutron energy spectrum of Lingenfelter, Canfield and Hampel. The average composition for terrestrial samarium is given.

Russ, G. P., III↗