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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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

ECCENTRIC MERGERS OF BLACK HOLES WITH SPINNING NEUTRON STARS

We study dynamical capture binary black hole–neutron star (BH–NS) mergers focusing on the effects of the neutron star spin. These events may arise in dense stellar regions, such as globular clusters, where the majority of neutron stars are expected to be rapidly rotating. We initialize the BH–NS systems with positions and velocities corresponding to marginally unbound Newtonian orbits, and evolve them using general-relativistic hydrodynamical simulations. We find that even moderate spins can significantly increase the amount of mass in unbound material. In some of the more extreme cases, there can be up to a third of a solar mass in unbound matter. Similarly, large amounts of tidally stripped material can remain bound and eventually accrete onto the BH—as much as a tenth of a solar mass in some cases. These simulations demonstrate that it is important to treat neutron star spin in order to make reliable predictions of the gravitational wave and electromagnetic transient signals accompanying these sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

SU-E-T-591: Measurement and Monte Carlo Simulation of Stray Neutrons in Passive Scattering Proton Therapy: Needs and Challenges

Purpose: Measure stray radiation inside a passive scattering proton therapy facility, compare values to Monte Carlo (MC) simulations and identify the actual needs and challenges. Methods: Measurements and MC simulations were considered to acknowledge neutron exposure associated with 75 MeV ocular or 180 MeV intracranial passively scattered proton treatments. First, using a specifically-designed high sensitivity Bonner Sphere system, neutron spectra were measured at different positions inside the treatment rooms. Next, measurement-based mapping of neutron ambient dose equivalent was fulfilled using several TEPCs and rem-meters. Finally, photon and neutron organ doses were measured using TLDs, RPLs and PADCs set inside anthropomorphic phantoms (Rando, 1 and 5-years-old CIRS). All measurements were also simulated with MCNPX to investigate the efficiency of MC models in predicting stray neutrons considering different nuclear cross sections and models. Results: Knowledge of the neutron fluence and energy distribution inside a proton therapy room is critical for stray radiation dosimetry. However, as spectrometry unfolding is initiated using a MC guess spectrum and suffers from algorithmic limits a 20% spectrometry uncertainty is expected. H*(10) mapping with TEPCs and rem-meters showed a good agreement between the detectors. Differences within measurement uncertainty (10–15%) were observed and are inherent to the energy, fluence and directional response of each detector. For a typical ocular and intracranial treatment respectively, neutron doses outside the clinical target volume of 0.4 and 11 mGy were measured inside the Rando phantom. Photon doses were 2–10 times lower depending on organs position. High uncertainties (40%) are inherent to TLDs and PADCs measurements due to the need for neutron spectra at detector position. Finally, stray neutrons prediction with MC simulations proved to be extremely dependent on proton beam energy and the used nuclear models and cross sections. Conclusion: This work highlights measurement and simulation limits for ion therapy radiation protection applications.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

Shock-wave studies of anomalous compressibility of glassy carbon

The physico-mechanical properties of amorphous glassy carbon are investigated under shock compression up to 10 GPa. Experiments are carried out on the continuous recording of the mass velocity of compression pulses propagating in glassy carbon samples with initial densities of 1.502(5) g/cm{sup 3} and 1.55(2) g/cm{sup 3}. It is shown that, in both cases, a compression wave in glassy carbon contains a leading precursor with amplitude of 0.135(5) GPa. It is established that, in the range of pressures up to 2 GPa, a shock discontinuity in glassy carbon is transformed into a broadened compression wave, and shock waves are formed in the release wave, which generally means the anomalous compressibility of the material in both the compression and release waves. It is shown that, at pressure higher than 3 GPa, anomalous behavior turns into normal behavior, accompanied by the formation of a shock compression wave. In the investigated area of pressure, possible structural changes in glassy carbon under shock compression have a reversible character. A physico-mechanical model of glassy carbon is proposed that involves the equation of state and a constitutive relation for Poisson’s ratio and allows the numerical simulation of physico-mechanical and thermophysical properties of glassy carbon of different densities in the region of its anomalous compressibility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Gas-Jet Method of Deposition of Nanostructured Silver Films

The synthesis of thin silver films by the gas-jet deposition method is experimentally and theoretically studied. When the metal is deposited onto silicon substrates from a supersonic jet of silver vapor with a helium carrier gas, nanostructured films with a 3−30 nm size of nanostructures are obtained for a 1230−1380 K range of jet source temperatures. The data on Ag–He gas-jet dynamics when it is expanded into vacuum (velocity, temperature, concentration, flux of particles onto a substrate) depending on parameters at the source (vapor temperature, flow rate of a carrier gas) are obtained by the method of direct simulation Monte Carlo. The range of optimal helium flow rates, when the efficiency of a gas-jet source is maximal, is determined. It is established that the presence of a background gas in a deposition chamber at pressure higher than 1 Pa decreases the flow of particles onto a substrate, and a simple way of its evaluation is proposed. Conditions for formation of silver clusters in the jet are determined by using the simulation. It is shown that for experimental deposition regimes there are no clusters in the jet, and the observed silver nanostructures are formed on the substrate surface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

One-Dimensional Nanostructures for Neutron Detection

This report consists of four parts in addition to a publication/presentation list. Part I is on electronic structure simulations on boron nitride (BN) and BC x N nanotubes using density function theory (DFT), Part II is on fabrication and characterization of nanowire sensors, Part III is on irradiation response of BN nanotubes using molecular dynamics (MD) simulations, and Part IV is on the in-situ transmission electron microscopy (TEM) study of irradiation response of BN nanotubes.

36 MATERIALS SCIENCE↗
DOE OSTI2016

X-ray-powered macronovae

A macronova (or kilonova) was observed as an infrared excess several days after the short gamma-ray burst GRB 130603B. Although the r-process radioactivity is widely discussed as an energy source, it requires a huge mass of ejecta from a neutron star (NS) binary merger. We propose a new model in which the X-ray excess gives rise to the simultaneously observed infrared excess via thermal re-emission, and explore what constraints this would place on the mass and velocity of the ejecta. This X-ray-powered model explains both the X-ray and infrared excesses with a single energy source such as the central engine like a black hole, and allows for a broader parameter region than the previous models, in particular a smaller ejecta mass ∼10{sup −3}--10{sup −2}M{sub ⊙} and higher iron abundance mixed as suggested by general relativistic simulations for typical NS–NS mergers. We also discuss the other macronova candidates in GRB 060614 and GRB 080503, and the implications for the search of electromagnetic counterparts to gravitational waves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Fe–K LINE TIME VARIABILITY AND Ni ABUNDANCE OF DISTANT REFLECTORS IN SEYFERT GALAXIES

We have performed systematic studies of narrow Fe–K line (6.4 keV) flux variability and Ni–K line intensity for Seyfert galaxies, using Suzaku and XMM-Newton archival data. Significant Fe–K line variability of several tens of percent was detected for a pair of observations separated by 1000–2000 days (Cen A, IC 4329 A, NGC 3516, and NGC 4151) and 158 days (NGC 3516). These timescales are larger by a factor of 10–100 than the inner radius of the torus, consistent with the view that X-ray reflection by a torus is a main origin for a narrow Fe–K line. The Ni–K line was detected with a >2σ level for the Circinus galaxy, Cen A, MRK 3, NGC 4388, and NGC 4151. A mean and variance of the Ni–Kα to Fe–Kα line intensity ratios are 0.066 and 0.026, respectively. Comparing this with the Monte-Carlo simulation of reflection, the Ni to Fe abundance ratio is 1.9 ± 0.8 solar. We discuss the results and the possibility of Ni abundance enhancement.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A UNIFORM CATALOG OF MOLECULAR CLOUDS IN THE MILKY WAY

The all-Galaxy CO survey of Dame et al. is by far the most uniform, large-scale Galactic CO survey. Using a dendrogram-based decomposition of this survey, we present a catalog of 1064 massive molecular clouds throughout the Galactic plane. This catalog contains 2.5 × 10{sup 8} solar masses, or 25{sub −5.8}{sup +10.7}% of the Milky Way's estimated H{sub 2} mass. We track clouds in some spiral arms through multiple quadrants. The power index of Larson's first law, the size-linewidth relation, is consistent with 0.5 in all regions—possibly due to an observational bias—but clouds in the inner Galaxy systematically have significantly (∼30%) higher linewidths at a given size, indicating that their linewidths are set in part by the Galactic environment. The mass functions of clouds in the inner Galaxy versus the outer Galaxy are both qualitatively and quantitatively distinct. The inner Galaxy mass spectrum is best described by a truncated power law with a power index of γ = −1.6 ± 0.1 and an upper truncation mass of M {sub 0} = (1.0 ± 0.2) × 10{sup 7} M {sub ⊙}, while the outer Galaxy mass spectrum is better described by a non-truncating power law with γ = −2.2 ± 0.1 and an upper mass of M {sub 0} = (1.5 ± 0.5) × 10{sup 6} M {sub ⊙}, indicating that the inner Galaxy is able to form and host substantially more massive GMCs than the outer Galaxy. Additionally, we have simulated how the Milky Way would appear in CO from extragalactic perspectives, for comparison with CO maps of other galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The formation of cores of giant planets at convergence zones of planetary migration

The formation of solid cores in giant planets of mass ∼10 M{sub ⊕} is numerically simulated following the scenario of Sándor et al. In this scenario, there are two convergence zones, corresponding to the outer and inner edges of the dead zone, where the torque exerted on planetary embryos by the gas nebula is zero. At the outer edge of the dead zone, anticyclonic vortices accumulate infalling dust aggregates, and planetary embryos are continuously formed in this scenario. We performed N-body simulations and show that massive objects of ≃10 M{sub ⊕} are formed in ∼2.5 Myr, starting from the embryos. The largest object is formed at the inner convergence zone, although planetary embryos are placed at the outer convergence zone. This is due to the scattering of embryos from the outer to the inner convergence zone, and the shorter damping timescale of eccentricity at the inner convergence zone compared to the outer one. We varied the migration timescale due to the torque from gas by changing the gas surface density around the convergence zones. We found that there is a critical migration timescale below which 10 M{sub ⊕}-sized objects are formed. Furthermore, we conducted simulations in which the gas surface density evolves according to viscous accretion. The largest object is also formed at the inner convergence zone irrespective of the strength of turbulence. Throughout the simulations, the location of the largest mass is the inner convergence zone. We confirmed that the formation timescale of a core of a Jovian planet can be explained in this scenario.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Infall of the Virgo Elliptical Galaxy M60 toward M87 and the Gaseous Structures Produced by Kelvin–Helmholtz Instabilities

We present Chandra observations of hot gas structures, which are characteristic of gas-stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located 1 Mpc east of M87. Chandra X-ray images at 0.5–2 keV show a sharp leading edge in the surface brightness that is 12.4 ± 0.1 kpc north and west of the galaxy center in the direction of M87 and characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of 1.00 ± 0.02 keV for an abundance of 0.5 Z{sub ⊙} inside the edge and 1.37{sub −0.19}{sup +0.35} keV for an abundance of 0.1 Z{sub ⊙} in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio n{sub in}/n{sub out}=6.44{sub −0.67}{sup +1.04} between gas inside the edge and in the cluster free stream region. If the edge is a cold front due solely to the infall of M60 in the direction of M87, we find a pressure ratio of 4.7{sub −1.4}{sup +1.7} and Mach number of 1.7{sub −0.3}{sup +0.3}. For 1.37 keV Virgo gas, we find a total infall velocity for M60 of v{sub M60}=1030±180 km s{sup −1}. We calculate the motion in the plane of the sky to be v{sub tran}=1012{sub −192}{sup +183} km s{sup −1}, implying an inclination angle of ξ=11{sub −3}{sup +3}°. Surface brightness profiles also show the presence of a faint, diffuse gaseous tail. We identify filamentary gaseous wing structures caused by the galaxy’s motion through the ICM. The structure and dimensions of these wings are consistent with simulations of Kelvin–Helmholtz instabilities, as expected if the gas-stripping is close to inviscid.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Electron Pre-acceleration at Nonrelativistic High-Mach-number Perpendicular Shocks

We perform particle-in-cell simulations of perpendicular nonrelativistic collisionless shocks to study electron heating and pre-acceleration for parameters that permit the extrapolation to the conditions at young supernova remnants. Our high-resolution large-scale numerical experiments sample a representative portion of the shock surface and demonstrate that the efficiency of electron injection is strongly modulated with the phase of the shock reformation. For plasmas with low and moderate temperature (plasma beta β{sub p}=5⋅10{sup −4} and β{sub p}=0.5), we explore the nonlinear shock structure and electron pre-acceleration for various orientations of the large-scale magnetic field with respect to the simulation plane, while keeping it at 90° to the shock normal. Ion reflection off of the shock leads to the formation of magnetic filaments in the shock ramp, resulting from Weibel-type instabilities, and electrostatic Buneman modes in the shock foot. In all of the cases under study, the latter provides first-stage electron energization through the shock-surfing acceleration mechanism. The subsequent energization strongly depends on the field orientation and proceeds through adiabatic or second-order Fermi acceleration processes for configurations with the out-of-plane and in-plane field components, respectively. For strictly out-of-plane field, the fraction of suprathermal electrons is much higher than for other configurations, because only in this case are the Buneman modes fully captured by the 2D simulation grid. Shocks in plasma with moderate β{sub p} provide more efficient pre-acceleration. The relevance of our results to the physics of fully 3D systems is discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

TRACING p -MODE WAVES FROM THE PHOTOSPHERE TO THE CORONA IN ACTIVE REGIONS

Atmosphere above sunspots is abundant with different types of waves. Among these waves are running penumbral waves in the chromosphere, quasi-periodic oscillations in the lower coronal loops, and recently reported running waves in sunspots’ photosphere, all of which were interpreted as magnetoacoustic waves by some authors. Are these waves in different atmospheric layers related to each other, what is the nature of these waves, and where are the ultimate sources of these waves? Applying a time–distance helioseismic analysis over a suite of multi-wavelength observations above a sunspot, we demonstrate that the helioseismic p -mode waves are able to channel up from the photosphere through the chromosphere and transition region into the corona, and that the magnetoacoustic waves observed in different atmospheric layers are a same wave originating from the photosphere but exhibiting differently under different physical conditions. We also show waves of different frequencies travel along different paths, which can be used to derive the physical properties of the atmosphere above sunspots. Our numerical simulation of traveling of waves from a subphotospheric source qualitatively resembles the observed properties of the waves and offers an interpretation of the shapes of the wavefronts above the photosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Control of synchrotron radiation effects during recirculation with bunch compression

Studies of beam quality during recirculation have been extended to an arc providing bunch compression with positive momentum compaction. It controls both incoherent and coherent synchrotron radiation (ISR and CSR) using methods including optics balance and generates little microbunching gain. We detail the dynamical basis for the design, discuss the design process, give an example, and provide simulations of ISR and CSR effects. Reference will be made to a complete analysis of microbunching effects.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

FaNGaS: a New Instrument for Fast Neutron Gamma Spectroscopy at FRM II Research Reactor at Garching

For the identification and quantification of actinides in radioactive packages, the non-destructive method of Prompt-Gamma Activation Analysis (PGAA) is applied. To investigate the inelastic (n, n 'γ) scattering, a new instrumentation was installed at the FRM II research reactor. It is designed to exploit the 10{sup 8} cm{sup -2}s{sup -1} neutrons at an average neutron energy of 1.9 MeV delivered by the SR10 beam line. The outgoing prompt γ-rays are measured utilizing a 50% efficiency HPGe detector. Since the cross sections are expected to be low for such a process, two related factors had to be taken into account for the design of the instrumentation: the high beam intensity at the sample position and the high signal-to-background ratio seen by the detector. Eventual low energy neutrons due to the multiple scatterings through the beam line can be minimized using collimators in the beam tube. This has also an effect to a prior neutrons and photons background reduction of the experimental environment. A higher efficiency of the counting can be achieved by the lowering of background at the detector. In this case, a heavy shielding for both neutrons and photons, is designed around the detector while optimizing the sample-detector distance. Monte-Carlo simulation studies were conducted to effectively design the fast neutron beam collimators and the detector shield. A detailed description of the setup characterization and results from simulations and experimental measurements will be discussed through this contribution. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Integrated X-ray detection system for determination of nuclear material concentration

An integrated system of X-ray Absorption Spectrometry (XAS), also called L-edge densitometry for uranium (LED) and X-ray Fluorescence spectrometry (XRF) is designed using Monte Carlo simulation for determining concentration of uranium and minor actinides for safeguard. The system can be useful to determination uranium and minor actinide, such as plutonium, neptunium, and etc., concurrently. The equipment is compact compared to the K-edge densitometer with high purity germanium detector which needs liquid nitrogen cooling since a low energy X-ray source is used. The system has been validated from simulation and analysis of the transmitted and reflected spectrum. The concentrations of nuclear material samples are obtained from this study. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Simulation of Spent Nuclear Fuel loading into a Final Waste Repository

Previous work towards studying repository loading have used: - spent nuclear fuel (SNF) with an average burnup composition; - a lumped capacitance thermal model for calculating temperature in a Cyclus repository model. The goal of this work is to improve on the repository models and use U.S. historical SNF inventory data in simulations to more accurately study the loading of a waste repository. These goals will be achieved by: - using UNF-ST-and-DARDS Unified Database (UDB) that has historic assembly-specific data (e.g, isotopic composition, heat) in Cyclus simulations; - implementing a more accurate thermal model within a Cyclus repository model. Objectives: - Create a Cyclus spent fuel conditioning model that packages spent fuel bundles into packages which have user-defined properties. - Create a Cyclus medium-fidelity repository model that gives accurate time and spatial dependent temperature values and loads the repository based on a user-selected loading strategy. Cyclus is an agent-based extensible framework for modeling flow of material through user-defined nuclear fuel cycles. In Cyclus, each facility in the fuel cycle is modeled individually and the facilities interact with one another as independent agents. The spent fuel conditioning model accepts spent fuel bundles and puts them into a cylindrical waste package. In the spent fuel conditioning model, the user can define variables: For each layer, radius, thermal conductivity, thermal diffusivity; For each package, Number of spent fuel bundles, Radius and height. The waste repository model accepts waste packages and emplaces them into available positions within the waste repository based on a thermal criteria. The thermal criteria is a temperature limit at the interface between the waste package surface and the host geology, that is set based on the repository's host geology. In the waste repository model, the user can define the variables: Capacity, Distance between waste packages, Distance between drifts, Repository host geology, Loading Strategy. After the addition of new waste packages at each time step, the waste repository model recalculates the temperature at each location in the repository. If the addition of this new package causes its temperature to exceed the thermal limit, it will be placed back into the buffer. A thermal model that relies on a transient 'outside' model and quasi-steady-state 'inside' model is used to accurately determine the temperature in the repository. The 'outside' model assumes a homogenous medium with the Engineered Barrier System (EBS) replaced by the geologic medium. Temperature solutions for the central waste package, adjacent point and line sources are superimposed to calculate the temperature at specific points in the repository. The central drift consists of one finite line source which represents the central waste package. The central drift also consists of point sources that represent neighboring waste packages in the central drift. The neighboring drifts are represented by infinite line sources. The 'inside' model is considered to be at a quasi-steady-state condition because EBS has a relatively low thermal mass compared to the infinite geologic medium. The steady state calculation is performed at each time step with the heat source and interface temperature as boundary conditions. Future Work: Run Cyclus simulations with U.S. historical SNF inventory data, the spent fuel conditioning and repository models to study how waste package acceptance strategies impact repository loading.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

CyBORG: An ORIGEN-Based Reactor Analysis Capability for Cyclus

One of the key weaknesses of many current nuclear fuel cycle simulation tools is in the inability to treat reactor-based materials feedbacks within fuel cycle systems. Rather, many of these tools rely on user-provided 'recipes' to describe the fission and transmutation of materials within a reactor. While sufficient for steady-state simulations (such as fuel cycle options at equilibrium), recipe-based models fall short when attempting to evaluate fuel cycle systems under transition. For example, within the context of the Fuel Cycle Options Evaluation and Screening Study, fuel cycle options such as EG29 (fast critical systems with a conversion ratio greater than unity which would drive thermal critical systems with recovered U and Pu) require physics-based treatments of materials within reactors in order to capture the full dynamics of material transformations within such actinide-based recycle scenarios. Similarly, other physics-based questions include system perturbations such as changing average fleet discharge burnup as well as accurate evaluations of available fuel materials to support fuel cycle transitions. In order to provide fuel cycle analysis the ability to evaluate these types of scenarios, a new ORIGEN-based reactor module for the Cyclus nuclear fuel cycle simulator is being developed known as CyBORG (Cyclus-Based ORiGen). CyBORG leverages recent modernization efforts in the Origen API to allow users to directly employ ORIGEN's validated depletion capabilities and extensive nuclear fuel data libraries in order to perform dynamic, physics-based reactor transformations to fuel materials within a fuel cycle simulation context. This paper will provide a summary of recent developments in this effort, including its present and proposed capabilities and overall design strategy. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Dose Mapping from a DD Neutron Generator at the University of Sharjah

The University of Sharjah recently acquired a model DD109.4M neutron generator from Adelphi Technology. The generator is moderated and has three neutron ports which are capable of providing fast and thermal neutrons. This neutron generator is intended to be used for various studies like neutron activation analysis, neutron imaging, and profiling and irradiation effects. It is imperative that appropriate measures are taken in order to minimize the radiation dose to the operators, students, and the public. The resulting dose must not exceed the limits set by the UAE Federal Authority for Nuclear Regulations (FANR) and the International Atomic Energy Agency (IAEA). The objective of this study is to generate a neutron and photon dose map of the generator room and its surrounding using simulations, experimentally verify this dose mapping, and set the operating and safety procedures for the neutron generator. (authors)

07 ISOTOPE AND RADIATION SOURCES↗