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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Modeling Astrophysical Explosions and Nucleosynthesis (Final Technical Report)

The goal of this project was to further our theoretical understanding of the extreme physics and heavy element nucleosynthesis occurring in stellar explosions, in particular supernovae and neutron star mergers. To study these systems, we further developed and applied numerical simulations (radiation hydrodynamical models and nuclear reaction networks) run on high performance computers. The numerical calculations and companion theoretical analysis helped to better define the sites of astrophysical nucleosynthesis, and make predictions of the associated observables (nucleosynthetic yields and electromagnetic signals) that can be used to anticipate and interpret experimental data. This project enhances the scientific value of the nuclear data obtained from current and future experimental facilities (e.g., rare isotope beams) by improving our understanding of the astrophysical context and specific physical conditions under which we expect such reactions to take place in Nature.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1981

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in massive stars

The production of heavy nuclei during explosive helium burning has been calculated using a hydrodynamical model of a 15-solar mass (Type II) supernova and an n-process nuclear reaction network. It is found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material, especially in the vicinity of Pt, nor are any actinides produced. These deficiencies reflect an inadequate supply of neutrons. However, some neutron-rich isotopes, normally associated with the r-process, are produced which may be significant for the production of isotopic anomalies in meteorites.

Blake, J. B.↗
NASA NTRS1993

Precision linear shaped charge severance of graphite-epoxy materials

This paper presents Precision Linear Shaped Charge (PLSC) components designed to sever a variety of target materials. Recent data for the severance of graphite-epoxy panels or targets with PLSC's are presented. A brief history of the requirement to originate the development of PLSC's for weapon components at Sandia National Laboratories is presented. The Department of Energy's (DOE) nuclear weapon systems have continually decreased in size. Today's relatively small weapons require the design of much more efficient, lighter, and smaller explosive components because fragments, air shocks, and pyro-shocks associated with the function of these components can damage electrical and other sensitive components located nearby. The DOE requirements for PLSC's are listed. Therefore, linear shaped charge (LSC) components for weapon systems can no longer be empirically or experimentally designed for a given application. Many of today's designs require severing concentric cylinders, for example, where the LSC jet is designed to sever only one of the two cylinders as was the case for the B90/Nuclear Depth Strike Bomb. Therefore, code modeling and simulation technology must be utilized to obtain a better understanding of the LSC jet hydrodynamic penetration, fracture, shear, and spall mechanisms associated with the severance of metallic as well as composite targets.

Vigil, Manuel G.↗
NASA NTRS1992

Analysis of the photospheric epoch spectra of type 1a supernovae SN 1990N and SN 1991T

This paper presents an LTE analysis of the photospheric epoch optical and IUE UV spectra of the recent Type Ia supernovae SN 1990N and SN 1991T. It is found that SN 1990N has matter moving as fast as 40,000 km/s, while SN 1991T has matter moving as fast as 20,000 km/s. The exponential density profile with e-folding velocity of 3160 km/s suggested by deflation and delayed/late-detonation explosion models is adequate for calculating fits to the observed spectra. Findings on the iron peak elements suggest that in both SNe some nuclear burning continues into the outer ejecta or the newly synthesized elements are mixed into the outer ejecta. The observed spectra of SN 1990N are consistent with a composition of the inner envelope like that of model W7. Intermediate-mass elements with abundances higher than solar are probably in the outer ejecta of both SNe, while silicon, sulfur, and calcium are underabundance in SN 1991T relative to SN 1990N by factors of order 3, 3, and 120, respectively.

Jeffery, David J.↗
DOE OSTI2020

Level Structure of {sup 31}S Via {sup 32}S({ital p,d}) {sup 31}S

Background: Properties of proton-unbound S-31 states determine the P-30(p, gamma) S-31 reaction rate, which has a significant impact on explosive hydrogen burning in classical novae and type-I x-ray bursts. Despite several previous studies, uncertainties still remain with respect to the nuclear structure of S-31 near the proton threshold. Purpose: The level structure of S-31 has been presently investigated via a charged-particle spectroscopy experiment using the S-32(p, d) S-31 reaction. Method: Deuterons corresponding to S-31 excited states with 3.285 <= E-x <= 10.8 MeV were momentum analyzed via an Enge split-pole spectrograph at six laboratory angles between 10 degrees and 62 degrees. Differential cross sections of the S-32(p, d)S-31 reaction were measured at E-p = 34.5 MeV. Distorted-wave Born approximation calculations were performed to constrain the spin-parity assignments of several of the observed levels. Results: We have detected 72 excited states of S-31, out of which 17 are within the astrophysical region of interest corresponding to the temperature range of 0.1-1.5 GK. We have resolved the discrepancy in the spin and parity of an excited state with E-x = 6542 keV, showing that is it not J(pi) = 3/2(-), and therefore the contribution of this state to the P-30(p, gamma) reaction rate is likely much less significant than previously thought owing to the larger angular-momentum transfer required to populate this excited state. Moreover, our measurement results help consolidate the spin-parity assignments for the 6377 and 6636 keV states in S-31. Conclusions: This work presents the most comprehensive spin-parity assignments to date from a single-neutron transfer reaction on S-32 to S-31 excited states in the region between 6 to 7 MeV excitation energy. This region is significant for the determination of the P-30(p, gamma)S-30 reaction rate over the temperatures characteristic of explosive hydrogen burning in novae.

Setoodehnia, K.↗
DOE OSTI2022

Assessment of the associated particle technique with high-resolution gamma-ray spectroscopy for in-field identification of chemical warfare agents and explosives

In this work, high-resolution prompt γ-ray neutron activation analysis (PGNAA) is performed using the associated particle (AP) technique with a deuterium-tritium neutron generator and high-purity germanium detector. Although the time resolution is inferior compared to similar systems employing fast scintillation γ-ray detectors, the strong background suppression combined with the high γ-ray energy resolution provides an important boost in sensitivity to certain key elements, especially relevant to field measurements of complex chemicals encased within thick layers of metal, such as in the case of recovered chemical warfare (CW) munitions. Results for various CW and explosive simulants contained within mock munitions are presented and compared with results obtained from traditional PGNAA measurements without the aid of the AP technique. Significant improvements in identification and discrimination between certain chemicals are achieved with the high energy resolution AP technique.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Report on the sensitivity kernel construction and updating the SPiRaL model with waveform data

The WAVEFORMS Initiative in the Ground-based Nuclear Detonation Detection (GNDD) program includes research leading towards the prediction of entire seismic and acoustic waveforms produced by natural and manmade events, including explosions. A key aspect of this research is the development of Earth (seismic) models at multiple scales including crustal, regional, and global. The work described here pertains to the global-scale seismic tomography effort led by LLNL.

58 GEOSCIENCES↗
DOE OSTI2025

Simultaneous imaging of vibrational, rotational, and electronic wave-packet dynamics in a triatomic molecule

Light-induced molecular dynamics often involve the excitation of several electronic, vibrational, and rotational states. Since the ensuing electronic and nuclear motion determines the pathways and outcomes of photoinduced reactions, our ability to monitor and understand these dynamics is crucial for molecular physics, physical chemistry, and photobiology. However, characterizing this complex motion represents a significant challenge when different degrees of freedom are strongly coupled. In this Letter, we demonstrate how the interplay between vibrational, rotational, and electronic degrees of freedom governs the evolution of molecular wave packets in the low-lying states of strong-field-ionized sulfur dioxide. Using time-resolved Coulomb explosion imaging (CEI) and quantum mechanical wave packet simulations, we directly map the bending vibrations of the molecule, show how the vibrational wave packet is influenced by molecular alignment, and elucidate the consequences of nuclear motion for the coupling between the two lowest electronic states of the cation. Furthermore, our results demonstrate that multicoincident CEI can be an efficient experimental tool for characterizing coupled electronic and nuclear motion in polyatomic molecules.

Atomic & molecular processes in external fields↗
DOE OSTI2023

Thermal Calculations to Determine Maximum Zircaloy Temperatures During Reactor Operations for Campaign 1 Fuel Assemblies

The H-Canyon Facility plans on processing bundles from Non-Aluminum Spent Nuclear Fuel (NASNF) Risk Group 1 (UO 2 core fuels). Uranium-zirconium (UZr) alloys and zirconium clad UO 2 fuel containing UZr intermetallic compound have the potential to cause explosions during dissolution. UZr intermetallic typically only forms when uranium and zirconium (or zirconium alloy) cladding are in contact at high temperatures. Thermal modeling was performed to determine the maximum cladding temperature for Campaign 1 Zircoloy cladded fuel assembles during reactor operation to help determine if the UZr intermetallic compound could have formed during reactor operations. The temperature of 350°C was chosen as a conservative minimum value for the possible formation of intermetallic UZr compound. The modeling approach, inputs, and results are outlined in this document.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Three-dimensional Hydrodynamic Simulations of Convective Nuclear Burning in Massive Stars Near Iron Core Collapse

Nonspherical structure in massive stars at the point of iron core collapse can have a qualitative impact on the properties of the ensuing core-collapse supernova explosions and the multimessenger signals they produce. Strong perturbations can aid successful explosions by strengthening turbulence in the postshock region. Here we report on a set of 4π 3D hydrodynamic simulations of O- and Si-shell burning in massive star models of varied initial masses using MESA and the FLASH simulation framework. We evolve four separate 3D models for roughly the final 10 minutes prior to and including iron core collapse. We consider initial 1D MESA models with masses of 14, 20, and 25 M ⊙ to survey a range of O/Si-shell density and compositional configurations. Further, we characterize the convective shells in our 3D models and compare them to the corresponding 1D models. In general, we find that the angle-average convective speeds in our 3D simulations near collapse are three to four times larger than the convective speeds predicted by MESA at the same epoch for our chosen mixing length parameter of α MLT = 1.5. In three of our simulations, we observe significant power in the spherical harmonic decomposition of the radial velocity field at harmonic indices of ℓ = 1–3 near collapse. Our results suggest that large-scale modes are common in massive stars near collapse and should be considered a key aspect of presupernova progenitor models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Multi-phenomenology Yield Characterization

This report serves as the first delivery of a four-year applied science effort to transform and advance the error bounds for the yield estimate of an explosion. Each year’s delivery will be in this form, culminating in the submission of this work for peer review to a scientific journal. Importantly, the yearly progress reports can then also be viewed as expanding drafts working towards a formal journal article submission. For the first tranche of funding, we collaborated with Air Force Technical Applications Center (AFTAC) scientists to identify unclassified real-world data that demonstrate and validate our advanced error propagation methods. Collaboration includes visits to AFTAC and telecons. For this development, we illustrate the fusion of seismic, acoustic, optical, and surface effect signatures from an explosion. The mathematics and code being adapted to this specific application (Williams et al., 2021) involves physics models of multiple sensor signatures. We have also identified related physics models and have integrated them into code. Current methods of underground explosion yield estimation for the Threshold Test Ban Treaty (TTBT) have served the US treaty monitoring mission well for decades. A research objective of the Defense Nuclear Nonproliferation Research and Development (DNN R&D) office of the National Nuclear Security Administration (NNSA) has always been to provide new technical capabilities for monitoring lower thresholds. The general model and error propagation code to be developed in this project is based on significant advances in error modeling and propagation needed to analyze data at lower detection thresholds. The second tranche of funding for this project began on May 1, 2022, and planned work for the second tranche includes: i) completing the integration of physical model code into the general error model framework; this code accommodates a wide range of linear/nonlinear source models, fixed/ random effects, and frequentist/Bayesian analyses (the purpose of which is not to dictate to users how to analyze data, but instead to allow users the maximum flexibility in their work); ii) illustrative application of code to identified data, and; iii) initial planning with AFTAC researchers on delivery of code to the Common Development Environment at AFTAC, and continued writing of the planned final journal article submission (year two of this progress report), with particular emphasis on descriptions of data identified for this effort.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2023

Comparing Early Evolution of Flames in X-Ray Bursts in Two and Three Dimensions

We explore the early evolution of flame ignition and spreading on the surface of a neutron star in three dimensions, in the context of X-ray bursts. We look at the nucleosynthesis and morphology of the burning front and compare to two-dimensional axisymmetric simulations to gauge how important a full three-dimensional treatment of the flame is for the early dynamics. Finally, we discuss the progress toward full-star resolved flame simulations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Three-dimensional Core-collapse Supernova Simulations with 160 Isotopic Species Evolved to Shock Breakout

We present three-dimensional simulations of core-collapse supernovae using the FLASH code that follow the progression of the explosion to the stellar surface, starting from neutrino radiation hydrodynamic simulations of the neutrino-driven phase performed with the Chimera code. We consider a 9.6 M ⊙ zero-metallicity progenitor starting from both 2D and 3D Chimera models and a 10 M ⊙ solar-metallicity progenitor starting from a 2D Chimera model, all simulated until shock breakout in 3D while tracking 160 nuclear species. The relative velocity difference between the supernova shock and the metal-rich Rayleigh–Taylor (R-T) "bullets" determines how the metal-rich ejecta evolves as it propagates through the density profile of the progenitor and dictates the final morphology of the explosion. We find maximum 56 Ni velocities of ~1950 and ~1750 km s -1 at shock breakout from 2D and 3D 9.6 M ⊙ Chimera models, respectively, due to the bullets' ability to penetrate the He/H shell. When mapping from 2D, we find that the development of higher-velocity structures is suppressed when the 2D Chimera model and 3D FLASH model meshes are aligned. The development of faster-growing spherical-bubble structures, as opposed to the slower-growing toroidal structure imposed by axisymmetry, allows for interaction of the bullets with the shock and seeds further R-T instabilities at the He/H interface. We see similar effects in the 10 M ⊙ model, which achieves maximum 56 Ni velocities of ~2500 km s -1 at shock breakout.

79 ASTRONOMY AND ASTROPHYSICS↗