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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Low-energy hydrogen uptake by small-cage C n and C n-1 B fullerenes

We present a theoretical study of the hydrogen uptake capability of carbon fullerene cages Cn and their boron-doped heterofullerene equivalents C n-1 B, with n = 20, 40, and 60, irradiated by hydrogen atoms in an impact energy range of 0.1–100 eV. In order to predict exohedral and endohedral hydrogen captures as well as the scattering probability of hydrogen for various cage types and sizes, we perform quantum-classical molecular dynamics (QCMD) calculations using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. Maximum endohedral hydrogen capture probabilities of 20% for n = 60 and 14% for n = 40 are found at impact energies close to 15 eV for both C n and C n-1 B systems. For n = 20, however, endohedral capture is observed at a maximum of 2%, while the exohedral capture reaches a maximum of 5% both at 15 eV. Similar results for the hydrogen capture are obtained by classical molecular dynamics based on the ReaxFF potential. Lastly, the stopping cross section per carbon atom from the QCMD simulations for all cage sizes displays a linear dependence on the projectile velocity with a threshold at 0.8 eV, and extrapolates well to the available theoretical data.

08 HYDROGEN↗
DOE OSTI2019

Interpreting mixing relationships in energetic melts to estimate vapor contribution and composition

Heterogeneous, glassy debris can be produced by energetic events such as near surface nuclear explosions and asteroid impacts. In these events, the resultant debris comprises a rapidly-cooled mixture of the projectile or bomb material with proximate materials such as soil and anthropogenic structures. Glasses formed in these events preserve inter and/or intra sample compositional variation reflecting complex mixtures of the precursor materials or their chemically fractionated products. Understanding formation mechanisms and chemical processes relating to energetic glass formation based on study of the end products requires an objective method for calculating the precursor components that mixed together to produce the final product. Here, we compare a set of multivariate linear-least squares approaches to address the unmixing problem of heterogeneous glasses including classical least squares (CLS), principal component analysis (PCA) and two multivariate curve resolution – alternating least squares (MCR-ALS) approaches. We generate a synthetic data set representing spatially resolved, compositional data in a set of heterogeneously mixed glasses to understand model sensitivity to precursor abundance and composition. We explore the impact of incomplete knowledge of the system prior to the formation of the melts on the resulting confidence and accuracy of the solution (i.e., the number, composition, and abundances of the precursor materials). We conclude that a closure and equality constrained MCR-ALS approach succeeds in identifying unrecognized precursor components and is a suitable alternative to CLS approaches when the investigator has incomplete knowledge of the starting precursor chemical compositions. Finally, we demonstrate application of this MCR-ALS approach to measurements of Trinitite.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

Asynchronous space–time domain decomposition method with localized uncertainty quantification

The computational cost associated with uncertainty quantification of engineering problems featuring localized phenomenon can be reduced by confining the random variability of the model parameters within a region of interest. Here in this case, a localized treatment of mesh and time resolutions is required to capture the effect of the confined material uncertainty on the global response. We present a computational approach for localized uncertainty quantification with the capability of asynchronous treatment of mesh and time resolutions. In particular, we allow each subdomain to have its local uncertainty representation and the corresponding mesh and time resolutions. As a result, computing resources can be directed toward a small region of interest where a model with high spatial and temporal resolutions is required. To verify the numerical implementation, we consider elastic wave propagation in an axially loaded beam. Moreover, we perform convergence studies with respect to the spatial and temporal discretizations as well as the size of an uncertain subdomain. A projectile impacting a composite sandwich plate is considered as an engineering application for the proposed method.

42 ENGINEERING↗
DOE OSTI2016

Investigation of the dynamic stress–strain response of compressible polymeric foam using a non-parametric analysis

Dynamic stress–strain response of rigid closed-cell polymeric foams is investigated in this work by subjecting high toughness polyurethane foam specimens to direct impact with different projectile velocities and quantifying their deformation response with high speed stereo-photography together with 3D digital image correlation. The measured transient displacement field developed in the specimens during high stain rate loading is used to calculate the transient axial acceleration field throughout the specimen. A simple mathematical formulation based on conservation of mass is also proposed to determine the local change of density in the specimen during deformation. By obtaining the full-field acceleration and density distributions, the inertia stresses at each point in the specimen are determined through a non-parametric analysis and superimposed on the stress magnitudes measured at specimen ends to obtain the full-field stress distribution. Furthermore, the process outlined above overcomes a major challenge in high strain rate experiments with low impedance polymeric foam specimens, i.e. the delayed equilibrium conditions can be quantified.

42 ENGINEERING↗
DOE OSTI2022

An arbitrary Lagrange-Eulerian investigation of HRAM shallow jet pre-spurt formation and time sensitivities to impact plate dynamics

With dry bay fires persisting as a significant contributor to aircraft vulnerability despite chronicled developments in survivability technologies, an accurate fire prediction capability remains paramount for credible vulnerability assessments. Physics based modeling of the hydrodynamic ram (HRAM) fluid deposition process is a key component of such capability, wherein capturing the first instance of fluid spurt, referred to herein as shallow jet spurts, is a core focus. Such pre-spurts as they have been formerly identified have only been witnessed sporadically in HRAM spurt experiments. In this work, ALE3D, a first-principles multi-physics code was employed to model the shallow jet spurt phenomenon with spherical projectiles impacting water-filled tanks faced with aluminum panels, such that the underlying physics and sensitivities could be explored. Development and verification of the 2D axisymmetric model is described relative to trends observed in a prior experimental campaign. Results from the verified model suggest shallow jet spurts have at least a quadratic sensitivity to the fundamental vibrational mode of the impact plate across impact velocities 610–1829 m/s (2000–6000 ft/s). It is further explained how shallow jet spurts are arrested for impacts at the two extremes of plate rigidity. This research constitutes the first fluid-structure modeling of shallow jet spurts which future three-dimensional analyses will expound upon.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Plasma production and composition from hypervelocity impacts on solar cell cover glass

Satellites are subjected to detrimental effects from the space environment, including impacts by orbital debris and meteoroids that can cause mechanical or electrical damage. While mechanical damage is well studied, electrical effects resulting from hypervelocity impact (HVI) remain poorly understood. In HVIs, where the projectile speed exceeds the speed of sound in the target material, the impact energy ionizes the material near the surface, creating a plasma that can cause radio frequency emission. This emission is the main source of electrical anomalies in satellites, but the mechanism behind its creation is still unknown. Ground-based experiments have been used to characterize HVI plasma, including the empirical power law relations that describe the impact charge produced as a function of impactor mass and speed. Quantifying these power law relations gives us a better understanding of the species formed in the impact which can eventually lead to plasma evolution models and help us first, understand the mechanism behind radio frequency emission and second, ways to prevent its damage to the satellites. In this paper, we interpret the results of the HVI experiments on solar cell coverglass targets and identify the potential chemical or molecular reactions that form the impact ion species. This is done by looking simultaneously at multiple data sets for different species within the same impact configuration, and using a new technique for quantifying the power law relations for each emitted species. We use time of flight analysis (TOF) to detect the charged particle compositions and determine their initial speeds. The results suggest that the charge production power law is species specific, with different formation mechanisms involved in a single HVI event, some of which are associated with dissociation and some with ionization of a molecule. Furthermore, our results also show that electrons have different power laws that depend on the spacecraft surface charge. TOF measurements of ions from impact events on solar cell cover glass shows the presence of SiO + and SiO – 2 as the dominant species present in plasmas on positively and negatively charged targets, respectively, as well as the formation of FeO + .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Preliminary study of radio frequency waves in hypervelocity impact plasma

Orbital debris and meteoroids can cause mechanical and electrical anomalies by impacting spacecraft. Although mechanical damage tends to occur only from particles with masses >10 –3 g, electrical damage can be a result of hypervelocity (> 10 km/s) impacts (HVI) even with smaller particles. In HVI, the projectile speed exceeds the speed of sound in the material and has enough energy to create plasma by ionizing the material near the surface, which can then emit radio frequency (RF) waves. In this paper, we conduct a preliminary study on the characteristics of impact-generated RF emission with the ultimate goal of building an RF predictive model for risk assessment of HVI electrical effects that can damage spacecraft. First, we introduce wavelet analysis as a method for denoising and quantifying the total RF signal energy. An appropriate mother wavelet and the number of decomposition levels are selected using a synthetic signal. Second, the total energy of the RF emission is calculated using Parseval’s theorem. Results suggest that the total RF signal energy is proportional to the energy flux of the impactor. Lastly, spectrograms of the RF emission are analyzed to characterize features that can be used in the future to predict impacts that can cause electrical damage to satellites.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Eulerian adaptive finite-difference method for high-velocity impact and penetration problems

Owing to the complex processes involved, faithful prediction of high-velocity impact events demands a simulation method delivering efficient calculations based on comprehensively formulated constitutive models. Such an approach is presented herein, employing a weighted essentially non-oscillatory (WENO) method within an adaptive mesh refinement (AMR) framework for the numerical solution of hyperbolic partial differential equations. Applied widely in computational fluid dynamics, these methods are well suited to the involved locally non-smooth finite deformations, circumventing any requirement for artificial viscosity functions for shock capturing. Application of the methods is facilitated through using a model of solid dynamics based upon hyper-elastic theory comprising kinematic evolution equations for the elastic distortion tensor. The model for finite inelastic deformations is phenomenologically equivalent to Maxwell s model of tangential stress relaxation. Closure relations tailored to the expected high-pressure states are proposed and calibrated for the materials of interest. Sharp interface resolution is achieved by employing level-set functions to track boundary motion, along with a ghost material method to capture the necessary internal boundary conditions for material interactions and stress-free surfaces. The approach is demonstrated for the simulation of high velocity impacts of steel projectiles on aluminium target plates in two and three dimensions.

Barton, Philip T.↗
DOE OSTI2011

Study of the fragmentation of a displacement cascade into subcascades within the Binary Collision Approximation framework

When a material is subjected to irradiation, many primary defects are created at the atomic level by sequences of ballistic collision events to form highly disordered regions defined as displacement cascades. The long term evolution of materials under irradiation is dictated by the number and the spatial distribution of the surviving defects in the displacement cascade. The peculiar power law shape of collision cross sections is responsible for the fractal feature of atomic trajectories set and then the fragmentation of a displacement cascade into smaller subcascades. We present a criterion to describe the fragmentation of a displacement cascade into subcascades and to calculate the volume fraction of subcascades in the overall cascade due to this fragmentation. Such a volume fraction then provides a natural framework to estimate the efficiency of different projectiles to induce phase transformation or amorphisation in solids under irradiation. From this definition of the fragmentation of a displacement cascade, this work gives some new insights to compare different irradiations performed with different particles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the local density dependence of electronic stopping of ions in solids

We use here time-dependent density functional theory to calculate the electronic stopping S e in binary Ni-Ni atomic collisions and for a Ni projectile along channeling directions in a Ni crystal. Our results show that when S e is reported as a function of the ground state target electronic density ρ 0 the stopping is not a single-valued function of the local density, as assumed in formalisms that date back to the origins of quantum mechanics, but shows loops, suggesting that it is inaccurate to model stopping as a dissipative force of the type F = β ( ρ 0 ) v , as it is customarily done in non-adiabatic molecular dynamics simulations of ion-solid interactions. We compare our results with S e in a uniform electron gas where the above definition for the force holds, and conclude on the validity of using jellium as a crude approximation for more realistic inhomogeneous electron gases.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

The FLUKA Code: Developments and Challenges for High Energy and Medical Applications

The FLUKA Monte Carlo code is used extensively at CERN for all beam-machine interactions, radioprotection calculations and facility design of forthcoming projects. Such needs require the code to be consistently reliable over the entire energy range (from MeV to TeV) for all projectiles (full suite of elementary particles and heavy ions). Outside CERN, among various applications worldwide, FLUKA serves as a core tool for the HIT and CNAO hadron-therapy facilities in Europe. Therefore, medical applications further impose stringent requirements in terms of reliability and predictive power, which demands constant refinement of sophisticated nuclear models and continuous code improvement. Some of the latest developments implemented in FLUKA are presented in this paper, with particular emphasis on issues and concerns pertaining to CERN and medical applications.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Compilation and Evaluation of Isomeric Fission Yield Ratios

Fission yields are essential data for reactor physics, forensics, and astrophysics. In some cases, the fission yield of a fragment is divided between the ground state and a long-lived excited state, and the relative population of the two states is referred to as the isomeric ratio. In this work, we present a comprehensive compilation of experimental isomeric fission yield ratios for all target and projectile combinations. When possible, these data are combined to provide recommended isomeric fission yield ratios for low energy neutron-induced fission and spontaneous fission. The recommended ratios are compared to the traditional Madland-England model, which attempts to describe the isomeric ratios with a single parameter relating to the angular momentum of the fragment. It is found that the model does not reliably reproduce isomeric ratios outside the few nuclei it was fitted to, and its simplified treatment of the statistical process following population in fission results in average spin values, which are neither constant nor follow a recently observed saw-tooth pattern.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Design and construction of a water target system for harvesting radioisotopes at the National Superconducting Cyclotron Laboratory

In this paper, a liquid water target system for harvesting radioisotopes at the National Superconducting Cyclotron Laboratory (NSCL) was designed and constructed as the initial step in proof-of-principle experiments to harvest useful radioisotopes from the Facility for Rare Isotope Beams (FRIB). FRIB will be a new national user facility for nuclear science, to be completed in 2020, at which radioisotopes will be collected synergistically from the water in cooling-loops for the primary beam dump that cycle the water at flow rates in excess of hundreds of gallons per minute. As part of the development of radiochemical expertise required to harvest long-lived radioisotopes of interest in this environment, the water target system described here was constructed and successfully used to collect a test beam of relativistic 24 Na ions produced at the NSCL. Finally, future studies will involve collecting interesting transition metal isotopes such as 67 Cu from less purified secondary projectile fragment beams.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2018

Application of the Generic Electronics for Time Projection Chamber ($\mathrm{GET}$) readout system for heavy Radioactive isotope collision experiments

Here we have implemented the Generic Electronics for Time Projection Chamber (GET) in a SAMURAI Pion Reconstruction and Ion-Tracker (SπRIT) readout system for heavy radioactive ion collision experiments at RIKEN-RIBF. The SπRIT experiment is designed for heavy ion collision experiments with radioactive ion beams, where a Time Projection Chamber (TPC) with 12096 pixelized readout pads is employed as the main device. Since the TPC is located on the beam line, the readout electronics must handle small signals from pions as well as very large signals from beam or large fragment particles. Operation of the GET electronics during experiment functioned well using 270 time-bucket readout with 25 MHz sampling at an event Data acquisition (DAQ) rate of 60 Hz. Using the slope information of acquired signals it is possible to extend the dynamic range of dE/dx information compared to using the peak height information. However, huge signals arising from energetic δ-rays produced by un-interacted projectiles induce dead channels, which can be recovered after 70 μs on average.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Experimental study of the 34 m Cl beam production at intermediate energies

Here the isomeric content of a 34 Cl beam produced in the intermediate-energy projectile fragmentation of a 150 MeV/u 36 Ar beam on a 3 mm-thick Be target was studied. β-delayed γ-ray spectroscopy was used to measure the population of 34 Cl fragments in the ground vs. isomeric states at zero degrees relative to the incoming primary beam for four different momentum settings of the fragment separator near the predicted central velocity of these fragments, as well as, at two non-zero-degree settings for one momentum setting. Of the settings explored, which excluded rigidities within 0.5% of the value predicted to maximize total 34 Cl yield due to unreacted primary beam, the maximum rate for the production of Cl was found at a rigidity setting 0.75% below the predicted peak 34 Cl yield. The maximum population of the isomeric state relative to the ground state was observed at a rigidity 1.25% below the predicted maximum 34 Cl yield. Studies such as this are important in generating the understanding needed for producing isomer-enriched rare-isotope beams.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Absolute efficiency response of the γ-ray spectrometer GRETINA for high-energy γ rays up to 6 MeV

GRETINA (Gamma-Ray Energy Tracking In-beam Nuclear Array), a state-of-the-art γ-ray tracking spectrometer, has been instrumental in advancing nuclear structure studies, particularly in experiments using fast beams of rare isotopes where the γ rays emitted in flight are subject to large Doppler shifts. This work presents an experimental determination of the γ-ray detection efficiency of GRETINA at energies up to 6 MeV. The high-energy γ rays originated from states that were populated in nucleon-removal reactions from a projectile beam at an intermediate beam energy of about 85 MeV/nucleon. Utilizing γ-γ coincidences, efficiency values were extracted in-beam and translated into a source efficiency at rest employing GEANT4 Monte Carlo simulations. A systematic discrepancy in the efficiency of the forward-positioned detectors was identified which is attributed to specific dead-time effects caused by high-energy light-particle events prevalent at forward angles, generating signals in the Ge crystals that saturate the preamplifier’s first stage. Furthermore, this study provides refined efficiency benchmarks for in-beam experiments, improving the accuracy of quantitative γ-ray spectroscopy analyses with GRETINA and GRETA (Gamma Ray Energy Tracking Array) in the future.

GRETINA↗
DOE OSTI2023

Investigating radioactive negative ion production via double electron capture

The relative cross sections for radioactive negative ion production via double electron capture have been measured for collisions between a 40 keV projectile beam of uranium-238 and potassium vapor. This was performed at the collinear resonance ionization spectroscopy (CRIS) experiment at CERN-ISOLDE and is a step towards measuring the electron affinities (EAs) of elements that cannot be efficiently produced in negative ion sources at radioactive ion beam (RIB) facilities. This includes short-lived radioactive isotopes that have low production quantities and heavy and superheavy elements that systematically have smaller EAs than work functions of available ion source materials. Negative ions are particularly sensitive to electron–electron correlation effects, which make such studies ideal for benchmarking atomic structure models that go beyond the independent particle model. While the EAs of most light elements have been measured, experimental investigations on heavier elements, namely the actinides, remain scarce due to their radioactive nature and production difficulty. By developing negative ion production by charge exchange, we aim to make these studies feasible at RIB facilities.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗