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DOE OSTI2026

A lumped particle direct simulation Monte-Carlo method combined with the collisional-radiative model for simulations of non-equilibrium laser-induced plasma plumes

Collisional plasma plumes induced by laser irradiation of material targets exhibit large variations in local density as well as ionization and excitation states, making purely hydrodynamic or kinetic simulations inaccurate or infeasible. To address this challenge and capture non-equilibrium effects in laser-induced plasma plumes at arbitrary degrees of ionization, we develop a hybrid computational approach that combines the kinetic direct simulation Monte Carlo (DSMC) method with a collisional-radiative model (CRM). This ℓDSMC-CRM approach utilizes a lumped particle method to represent minor fractions of excited ions in particle-based simulations and a special coarse-graining technique for atomic spectra and photoionization rates, ensuring numerical convergence at reduced computational cost. The hybrid approach is applied to simulate spatially homogeneous relaxation as well as one- and two-dimensional expansions of plasma plumes induced by irradiation of a copper target by a nanosecond laser pulse in a vacuum or background gas. The comparison with an equilibrium model, where local Saha-Boltzmann equilibrium is enforced, shows that the non-equilibrium effects play a dominant role. The equilibrium model can fail to predict the flow structure and strongly underestimate the degree of absorption of laser radiation by the plume. The ℓDSMC-CRM approach is validated against experimental data demonstrating reasonable agreement with the experimental electron density and temperature, while the equilibrium model is found to dramatically underestimate electron density and temperature. The flexibility of the ℓDSMC-CRM approach allows for its seamless integration into existing DSMC frameworks, making it a valuable tool for high-fidelity plasma modeling in laser-material interactions, laser-based manufacturing, and beyond.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2026

Process-driven roadmap for depositing super duplex stainless steel via wire Arc additive manufacturing

Here, this study systematically investigates the effects of shielding gas, bead spacing, weld mode, and travel speed on the phase balance, porosity, and hardness of wire arc additively manufactured (WAAM) super duplex stainless steel (ER2594). Robotic WAAM was employed to fabricate multilayer walls under systematically varied process conditions, followed by phase transformation simulations, X-ray computed tomography (XCT), electron backscatter diffraction (EBSD), and microhardness evaluation. Thermodynamic simulations predicted rapid cooling of AM process can suppress the potential formation of deleterious precipitates which was later validated via cross-sectional microstructure analyses of printed samples. XCT revealed porosity levels below 0.2% for all deposits, with reduced travel speed significantly lowering defect volume. Microstructural analyses revealed the evolution of various austenite precipitates, including grain boundary austenite (GBA), Widmanstätten austenite (WA), and intergranular austenite (IGA), sequentially upon cooling of the ferrite phase. Among all process parameters, weld transfer mode exhibited the strongest influence on phase balance; pulsed mode promoted higher ferrite retention (~ 36%) compared to RapidX mode. No consistent relationship between stabilized phase fraction and captured microhardness was observed. This work provides critical insights for optimizing WAAM parameters to control phase balance and mechanical performance, which is essential for producing high-integrity super duplex stainless-steel components for nuclear and marine applications.

Grain orientation↗

DOE OSTI2024

Comparative characterization of mixed spectra and thermal neutron shielded irradiated tungsten

The effect of mixed spectra and thermal neutron shielded irradiation on tungsten was evaluated with plasma exposure in the tritium plasma experiment followed by thermal desorption spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The two different irradiation campaigns were performed at the High Flux Isotope Reactor to 0.39–0.74 displacement per atom (dpa) in the 894–1379 K temperature range. A neutron spectrum influence on the void size and void number density was not observed. However, a strong correlation was found between void size and void number density with temperature, but not with dpa in the limited dpa range of this study. Thermal neutron shielding significantly reduced the transmutation to Re+Os. Higher irradiation temperature will lead to larger voids with lower number density, which reduces deuterium retention. In conclusion, grain growth was also observed for high-temperature irradiation of over ~1300 K within the limited grains visible in the transmission electron microscopy specimens.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Designing a boron nitride polyethylene composite for shielding neutrons

Neutrons are encountered in many different fields, including condensed matter physics, space exploration, nuclear power, and healthcare. Neutrons interacting with a biological target produce secondary charged particles that are damaging to human health. The most effective way to shield neutrons is to slow them to thermal energies and then capture the thermalized neutrons. These factors lead us to consider potential materials solutions for neutron shields that maximize the protection of humans while minimizing the shield mass and adapt well to modern additive manufacturing techniques. Using hexagonal boron nitride (hBN) as a capture medium and high-density polyethylene (HDPE) as a thermalization medium, we aim to design the optimal internal structure of h 10 BN/HDPE composites by minimizing the effective dose, which is a measure of the estimated radiation damage exposure for a human. Through Monte Carlo simulations in Geant4, we find that the optimal structure reduces the effective dose up to a factor of 72 over aluminum (Al) and up to a factor of 4 over HDPE; this is a significant improvement in shielding effectiveness that could dramatically reduce the radiation exposure of occupational workers.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Optimizing Layered Control Strategies for Reducing Exposure to SARS-CoV-2

While there is growing understanding of the predominance of the airborne mode of transmission of the SARS-CoV-2 virus, there is a lack of guidance on how to build an effective system of controls to mitigate transmission in enclosed spaces. Such a system integrates multiple hazard-specific control measures to both eliminate or replace a hazard, and safeguard individuals against potential exposure and infection. Controls are defined by the US Occupational Safety and Health Association (OSHA) as the use of engineering methods to reduce the level of hazard inside a confined space. The Hierarchy of Controls provides a framework through which a system of controls can be examined; identifying those which directly remove or replace a hazard as the most effective, and individual behavioral measures (e.g., masking or shielding) as least effective. Use of such a framework to quantify control effectiveness might allow for the promotion of spaces as meeting a certain threshold of safety, likely adding to the confidence of space users resulting in increases in various metrics such as sales, visits, or likes.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2023

Monte Carlo simulation of shielding designs for a cabinet form factor preclinical MV–energy photon FLASH radiotherapy system

Purpose: A preclinical MV-energy photon FLASH radiotherapy system is being designed at Stanford and SLAC National Accelerator Laboratory. Because of the higher energy and dose rate compared to conventional kV-energy photon laboratory-scale irradiators, adequate shielding in a stand-alone cabinet form factor is more challenging to achieve. We present a Monte Carlo simulation of multilayered shielding for a compact self-shielding system without the need for a radiation therapy vault. Methods: A multilayered shielding approach using multiple alternating layers of high-Z and low-Z materials is applied to the self-shielded cabinet to effectively mitigate the secondary radiation produced and to allow the device to be housed in a Controlled Radiation Area outside of a radiation vault. The multilayered shielding approach takes advantage of the properties of high-Z and low-Z radiation shielding materials such as density, cross-section, atomic number of the shielding elements, and products of radiation interactions within each layer. The Monte Carlo radiation transport code, FLUKA, is used to simulate the total effective dose produced by the operation. Results: The multilayered shielding designs proposed and simulated produced effective dose rates significantly lower than monolayer designs with the same total material thickness at the regulatory boundary; this is accomplished through the manipulation of the locations where secondary radiation is produced and reactions due to material properties such as neutron back reflection in hydrogen. Borated polyethylene at 5 wt% significantly increased the shielding performance as compared to regular polyethylene, with the magnitude of the reduction depending upon the order of the shielding material. Conclusions: The multilayered shielding provides a path for shielding preclinical FLASH systems that deliver MV-energy bremsstrahlung photons. Furthermore, this approach promises to be more efficient with respect to the shielding material mass and space claim as compared to shielded vaults typically required for clinical radiation therapy with MV photons.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2025

Warpage-Resistant, Under-Extrusion-Free, High-Surface-Quality Additive Manufacturing Process for Polyethylene-Based Composite Radiation Shielding Material

Polyethylene (PE) is one of the best shielding materials for primary space radiation due to its high hydrogen content. For effective secondary neutron shielding, boron-rich fillers are incorporated to enhance performance. The semicrystalline nature and high thermal expansion coefficient of PE impede its adoption for in situ additive manufacture in space via the fused deposition modeling (FDM) 3D printing. Here, we developed an optimized PE blend to mitigate the effects of under-extrusion and warpage. Guided by studies on extrusion and warpage, we developed an optimal set of printing parameters for the proposed PE blend. The optimum PE blend─both in its pure form and when doped with fillers─has been tested on different FDM printers. The printed structures exhibit high and uniform density, smooth surfaces, no warpage, and competitive mechanical properties. The FDM-printed plates demonstrate efficient shielding from thermal neutrons, predicted via modeling and confirmed experimentally using extended Q-range small-angle neutron scattering.

additive manufacturing↗

DOE OSTI2025

A Thorough Characterization of the Tellurocyanate Anion

Tellurocyanate, [TeCN] − , is the heaviest group 16 congener of the cyanate anion, [OCN] − . Due to the relative instability of the C─Te bond, tellurocyanate chemistry has seen only scarce attention. Here, we present the facile synthesis and thorough characterization of [K@crypt-222][TeCN]. The anion is essentially linear with interatomic distances C─N = 1.150(6)Å and C─Te = 2.051(4)Å, thus approximating a C≡N triple bond and for C─Te a bond order between 1 and 2. Fully 13 C and 15 N labeled [Te 13 C 15 N] − allowed for the extraction of chemical shifts and all possible coupling constants ( 13 C = 77.8 ppm, 15 N = 285.7 ppm, 125 Te = −566 ppm, 1 J 13C-15N = 8 Hz, 1 J 13C-125Te = 748 Hz, 2 J1 5N-125Te = 55 Hz), which were also determined independently by quantum chemical calculations. In the series [ChCN] − (Ch = O─Te), [TeCN] − shows the strongest spin-orbit coupling (SOC) induced heavy-atom effect on the light-atom shielding (SO-HALA-effect). In contrast, 15 N shifts are also well described without considering relativistic effects and/or SOC. Negative-ion photoelectron spectroscopy was used to extract the electron affinity (EA = 3.034 eV) and spin-orbit splitting (3807 cm −1 ) of [TeCN] • . These values continue the trends of falling EA and rising SOC in the series [ChCN] • .

Bonding analysis↗

DOE OSTI2020

An experimental investigation of the effectiveness of Ar-CO 2 shielding gas mixture for the wire arc additive process

Wire arc additive manufacturing (AM) is the process by which a large, metallic structure is built layer-by-layer using a welding arc to melt a wire feedstock. A novel opportunity exists to alter the shielding gas composition to fabricate distinct geometrical features without altering the other AM parameters. In this paper, shielding gases with varied concentrations of Argon (Ar) and CO 2 was used to deposit three distinct geometric shapes (walls, infill, and overhang) using a wire-based additive manufacturing system utilizing the gas metal arc welding (GMAW) surface tension transfer (STT) process. Computer-aided design (CAD) models were sliced with a custom-built slicer, and the sliced algorithm was converted into optimal robotic toolpaths. A custom virtual instrument (VI) was built in LabVIEW to compare the temperature profiles on the surface during each deposition process. After each deposition, the geometric features were scanned, and the surface waviness value was evaluated. Tensile and Charpy impact coupons were extracted from the wall geometries in the longitudinal and transverse directions and tested. The results indicated that a higher CO 2 content produced higher melt pool temperatures to an extent, while lower contents of CO 2 resulted in a dimensionally accurate geometry. The data also indicated that the 2%/98% CO 2 /Ar blend produced scatter in tensile strength and the analysis of variance (ANOVA) shows significant difference. However, the intermediate range of CO 2 (5–10%) resulted in uniform tensile properties. Altogether, these results indicate that a 5%/95% CO 2 /Ar blend is the ideal shielding gas for lowering process temperatures and improving mechanical properties in wire arc additive manufacturing using the gas metal arc welding surface tension transfer process. Additionally, varying concentrations of Ar/CO 2 can be used within the same part in order to modify the local properties or process parameters such as strength, toughness, temperature, or dimensional features. This may improve overall manufacturing quality without sacrificing specific properties.

42 ENGINEERING↗

DOE OSTI2022

Efficient microwave absorption with V n+1 C n T x MXenes

The availability of MXenes and other two-dimensional conductive nanomaterials with tunable surface chemistry has reshaped the field of electromagnetic protection. However, the high electrical conductivity and low dielectric loss of titanium-based MXenes lead to strong reflection of electromagnetic waves, even when combined with polymers to form composites. Here, we report on the ability of vanadium-based MXenes to provide broadband microwave absorption. Polyurethane composites with ~2 wt % V n+1 C n T x can absorb 90% of electromagnetic waves covering the entire X band. In addition, pure V n+1 C n T x films of submicrometer thickness can provide effective electromagnetic interference shielding. The free electron transport, surface terminations, native defects, and layers arrangement in composites have profound effects on electronic and dielectric properties of V n+1 C n T x MXenes. This study points toward a new frontier for development of thin and highly absorbing MXene-based electromagnetic protection materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2025

Correct Interpretations of ENDF-102 Definitions for Resonance Effects

My Uncle Willie circa 1600 wrote “What’s in a name; a rose by any other name would smell as sweet.” I fear in this case we have a somewhat similar problem in that we may be using the same word but are not using the same definition; specifically, the word Unresolved. The simplest physics definition as it applies to neutron resonances, is the energy point where we can no longer see/measure ALL – let me repeat that – ALL - of the individual resonances. That seems simple and clear, but the question is: how to represent resonances beyond this point in order to accurately reproduce the effects we have seen in measurements and expect/need to reproduce in our applications. We know there are more, unseen resonances, otherwise we wouldn’t say Unresolved. The ENDF approach is well defined in ENDF-102 and simple: for ENDF data the only way to represent Unresolved data is by using a theoretical model to define the distribution of resonances, including those that are too narrow to measure (i.e., are unresolved). It is important to note that in ENDF this is the one and only Unresolved model, e.g., there is no provision in ENDF to accurately define individually ALL resonances above the Resolved energy range – by ALL here I mean both those that we can measure and those that we cannot individually measure, but that theory and integral measurements tells us are present. An alternative approach, which would appear to be equally valid, would be to include the latest measured data as tabulated energy expendent data extending upwards in energy above the Resolved energy range. In this approach the evaluation would not include an ENDF style Unresolved energy range; it would only include a Resolved resonance region, followed by tabulated higher energy points, representing the resonances that could be measured beyond the Resolved range. But an important point to note: By listing these resonances above the resolved energy one admits that at least some resonances in this energy range are missing as Unresolved; i.e., they are too narrow or overlapping to measure. The purpose of this paper is to illustrate that the later approach, while done with good intentions, and appearing to be valid/adequate in plots, does not meet the need of our engineering applications. Why? As we will see below, of these two possible approaches, only the ENDF use of a model to statistically include the missing, i.e., unresolved, resonances, can meet our engineering needs to reproduce the integral effects we have measured and understand. Only with this statistical model can we predict and include in our calculated results the important effects of temperature (Doppler broadening), and energy integrals (self-shielding). Below I will first present results using two ENDF/B-VIII.1 evaluations, U235 and U238, that use the correct ENDF-102 definition of an Unresolved resonance region, using a statistical model to include the effects of resonances that theory predicts are present, but are too narrow to measure. These two evaluations reproduce the expected temperature (Doppler) and energy integral (self-shielding) effects that we expect. Next I will present results using one ENDF/B-VIII.1 evaluation, 26-Fe-56, that does not use an ENDF-102 Unresolved resonance region; instead above its Resolved energy range it lists many tabulated energy points, that look like measured data, but by definition, since they are included above the ENDF Resolved energy range there are missing Unresolved resonances, i.e., there are missing the resonances that are too narrow to resolve, i.e., are unresolved. My conclusion, and I hope yours, is that the below figures illustrate that this approach does not reproduce the temperature and energy integrals that we expect and need to accurately calculate results for our fission reactor calculations. As such this approach should not be used in ENDF formatted evaluations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Role Evaluation of Active Groups in Lignin on UV-Shielding Performance

The contribution of the active groups in lignin to ultraviolet (UV)-shielding performance still remains unclear. In this study, we employed 16 lignin model compounds and theoretical calculations to ascertain the contribution of different functional groups to UV-shielding performance. These results showed that the order of UV-shielding performance on functional groups was -C=C–CHO > -C=C–COOH > -C=C–CH 2 OH > --C=C > quinone > -COOH > -OCH 3 ≈ -OH. Moreover, the synergism between the para-substituted electron-donating group -OH and the electron-withdrawing group allyl on the aromatic ring played a major role in UV-shielding performance of lignin models, whereas the additive effect of meta/ortho-substituted -OCH 3 played a secondary role. Furthermore, we found that the hydrophile–lipophile balance (HLB) value of lignin models also greatly affected the sunscreen protection factor (SPF) of lignin model-based sunscreens. A closer HLB value of lignin to 8.89 corresponded with a higher SPF of the lignin model-based sunscreen. The commercial photoprotective ingredient ethylhexyl methoxycinnamate (EHMC) and lignin models had a synergistic effect on UV-shielding performance caused by the π–π stacking interaction between the parallel-displaced stacked aromatic rings of lignin models and EHMC. Additionally, the UV irradiation test showed that these sunscreens prepared using lignin models and EHMC exhibited good photostability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Unresolved resonance region cross section measurements and validation [Slides]

This presentation discusses the ENDF format and its implication for experimental data. The effect of self-shielding on measured cross sections some call this effect transmission enhancement (to be explained). Additionally discussed: from experiment to evaluation. And finally, Processing “high energy resolution” transmission for URR evaluation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

E-PiPEline: Face Shields and Face Coverings Using Commonly Available Materials

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2020

E-PiPEline: Quick to Market Face Coverings and Face Shields Using Commonly Available Materials

The Center for Disease Control has recommended that the public should wear cloth face coverings in public settings. Face coverings and face shields can be made by using Commonly Available Materials (CAMs). As part of the Sandia COVID-19 LDRD effort (funded under the Materials Science Investment Area), the Sandia E-PiPEline task evaluated design options for face coverings and face shields considering their effectiveness, durability, build difficulty, build cost, and comfort. Observations from this investigation are presented here to provide guidelines for home construction of face coverings and face shields. This executive summary includes a brief roadmap of the analysis methodology, two one-page handouts geared to be distributed to the public at large (one for face coverings and one for face shields), and additional observations regarding potential solutions for face coverings and face shields included to further support the one-page handouts.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

E-PiPEline: Quick to Market Emulated-PPE using Commonly Available Materials

The Center for Disease Control has recommended the public to wear cloth face coverings in public settings that reduce potential exposure to COVID-19 where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially in areas of significant community based transmission. These face coverings and other Emulated-Personal Protective Equipment (EPPE) can be made by using Commonly Available Materials (CAMs). As part of the Sandia COVID-19 LDRD effort (funded under the Materials Science Investment Area), the Sandia E-PiPEline task evaluated E-PPE design options for face coverings and face shields considering their effectiveness, durability, build difficulty, build cost, and comfort. Observations from this investigation are presented here to provide guidelines for home construction of E-PPE. This executive summary includes a brief roadmap of the analysis methodology, two one-page handouts geared to be distributed to the public at large (one for E-PPE face coverings and one for E-PPE face shields), and additional observations regarding the potential solutions for E-PPE face coverings and face shields included to further support the one-page handouts.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2026

Shock wave formation in the thermosphere by an earthgrazing fireball: Empirical evidence for volatile-enhanced hydrodynamic shielding

Hydrodynamic shielding is a theoretically well-established but observationally elusive and experimentally difficult-to-replicate phenomenon with implications that extend far beyond meteor physics. Rare earthgrazing meteoroids with infrasound signatures that penetrate to the ground can be used to probe hydrodynamic shielding that leads to strong shock formation at high altitude. Here, we report the first coordinated optical and multi-station infrasound observations of a centimeter-scale earthgrazing fireball that generated sustained cylindrical line shock at thermospheric altitudes near 92 km. The event was recorded by numerous optical stations and three infrasound arrays, allowing trajectory reconstruction, ablation behavior, acoustic source localization, and shock characteristics. Optical observations indicate early mechanical erosion and ablation/evaporation at exceptionally low dynamic pressure, consistent with a cometary or a porous, volatile-bearing CM chondritic object. Independent infrasound detections localize shock generation to multiple points along a 164 km trajectory segment near perigee. Weak-shock modeling yields a consistent blast radius of ∼30 m, implying an acoustic-equivalent source size far exceeding the physical dimensions of the ∼45 g nucleus. We demonstrate that classical gas dynamics and ablation-driven hydrodynamic shielding alone cannot account for these observations under ambient thermospheric conditions. We show that volatile release provides the additional flow-field density enhancement required to amplify hydrodynamic shielding, reduce the effective local Knudsen number, and sustain a shock envelope capable of radiating detectable infrasound. Furthermore, these results demonstrate that small, volatile-rich meteoroids can transiently establish continuum-like flow in rarefied environments.

Astrometry↗

DOE OSTI2022

Structure/Interface Coupling Effect for High-Voltage LiCoO 2 Cathodes

LiCoO 2 (LCO) is widely applied in today's rechargeable battery markets for consumer electronic devices. However, LCO operations at high voltage are hindered by accelerated structure degradation and electrode/electrolyte interface decomposition. To overcome these challenges, co-modified LCO (defined as CB-Mg-LCO) that couples pillar structures with interface shielding are successfully synthesized for achieving high-energy-density and structurally stable cathode material. Benefitting from the "Mg-pillar" effect, irreversible phase transitions are significantly suppressed and highly reversible Li + shuttling is enabled. Interestingly, bonding effects between the interfacial lattice oxygen of CB-Mg-LCO and amorphous Co x B y coating layer are found to elevate the formation energy of oxygen vacancies, thereby considerably mitigating lattice oxygen loss and inhibiting irreversible phase transformation. Meanwhile, interface shielding effects are also beneficial for mitigating parasitic electrode/electrolyte reactions, subsequent Co dissolution, and ultimately enable a robust electrode/electrolyte interface. As a result, the as-designed CB-Mg-LCO cathode achieves a high capacity and excellent cycle stability with 94.6% capacity retention at an extremely high cut-off voltage of 4.6 V. We report these findings provide new insights for cathode material modification methods, which serves to guide future cathode material design.

25 ENERGY STORAGE↗