Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Neutron Spectra”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Generation of the TSL for Zirconium Hydrides from Ab Initio Methods

Zirconium hydride (ZrHx) is a moderator material used in TRIGA and other reactors that may exist in multiple phases with varying stoichiometry, which include the δ phase and the ϵ phase. Current ENDF/B-VIII.0 ZrHx thermal scattering law (TSL) evaluations do not distinguish between phases. These sub-libraries were generated with the LEAPR module of NJOY using historic phonon spectra derived from a central force model and assume incoherent elastic scattering for both bound hydrogen and zirconium, which neglects the effects of crystal structures important for scattering from zirconium bound in ZrHx. In this work, the TSLs for hydrogen and zirconium bound in δ-ZrHx and ϵ-ZrH2 were generated from phonon spectra derived from modern ab initio lattice dynamics methods and ab initio molecular dynamics. Subsequently, TSLs for hydrogen and zirconium in ZrHx and ZrH2 were generated using the Full Law Analysis Scattering System Hub (FLASSH) code. The built-in generalized coherent elastic routine was used to generate the previously neglected elastic contribution from zirconium for this material. The present TSLs provide both a re-evaluation of the current ZrH sub-libraries and expansion of the set of TSLs available for the examination of neutrons in systems with zirconium hydride, permitting explicit treatment of δ and ϵ phases.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Inclusive breakup cross sections in reactions induced by the nuclides 6 He and 6,7 Li in the two-body cluster model

Calculations of inclusive α particle production are performed to interpret reaction experimental data induced by the two-neutron halo 6He and the isotopes 6,7 Li on different target nuclei. In this work, we have implemented the zero-range post-form DWBA to compute the elastic and nonelastic breakup cross sections. Integrated cross sections, angular distributions and spectra are presented. Projectiles are approximated as two-body clusters, namely 6 He as α+dineutron and 6 Li ( 7 Li) are interpreted as α+deuteron(triton). The São Paulo optical potential is employed in the calculation of the distorted wave functions for the incident channels, while standard phenomenological interactions are taken for the fragment-target interactions. Calculations for 6 Li and 7 Li furnish a good description of the data, while the reaction involving 6 He is found to be more complicated, where interpretation of the data must still be considered incomplete. The present analysis identifies an overall large contribution from inclusive breakup emission for all the cases studied.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

The hypernuclear physics program at Jefferson Lab

Missing mass spectroscopy of Λ hypernuclei using the (e, e' K⁺) re action has been performed in the past at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) by several experiments in Halls A and C. A new experimen tal campaign is expected to start running in 2026 in Hall C and to provide the first study of the isospin dependence in medium-mass hyperisotopes by populating $^{40}_Λ{K}$ and $^{48}_Λ{K}$ using isotopically enriched calcium targets [E12-15-008]. During this cam paign, it will be possible to study Λ interactions in nuclear matter using a lead target [E12-20-013]. Solid-state targets made of lithium, beryllium, boron [LOI12-23-013], and aluminum [LOI12-23-016] are considered to be included in the campaign. The use of the HKS and HES spectrometers together with thin target foils and high beam currents leads to a sub-MeV energy resolution, significantly better than in hadron beam experiments. Valuable information on few-body hyperon systems would be gained if helium targets were used [E12-19-002]. Using an additional spectrometer for measuring the decay-pion spectra could give access to the binding energies of light hyperfragments [LOI12-23-011]. The measurement of precise and accurate en ergy spectra of different hyperisotopes probes the Λ-N interaction in nuclei including the Λ-N-N interaction. The latter is assumed to play a key role for the stiffness of the nuclear equation of state relevant for the stability of neutron stars.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1991

A disc-reflected component in the spectra of X-ray bursters

An argument is presented to the effect that a disk-reflected component should be present in the spectra of X-ray bursts and is best seen just after the burst peak when the reflected photons, delayed by their passage to the site of reflection, appear in stronger contrast to the fast-declining primary emission from the cooling neutron star. It is shown that disk reflection has an observable effect on the spectrum of the burst tail. The possible use of the concomitant absorption edge as a diagnostic of the accretion disk is discussed.

Day, C. S. R.↗
NASA NTRS1995

High LET, passive space radiation dosimetry and spectrometry

The development of high linear energy transfer (LET), passive radiation dosimetry and spectrometry is needed for the purpose of accurate determination of equivalent doses and assessment of health risks to astronauts on long duration missions. Progress in the following research areas is summerized: intercomparisons of cosmic ray equivalent dose and LET spectra measurements between STS missions and between astronauts; increases LET spectra measurement accuracy with ATAS; space radiation measurements for intercomparisons of passive (PNTD, TLD, TRND, Emulsion) and active (TEPC, RME-111) dosimeters; interaction of cosmic ray particles with nuclei in matter; radiation measurements after long duration space exposures; ground based dosimeter calibrations; neutron detector calibrations; radiation measurements on Soviet/Russian spacecraft; space radiation measurements under thin shielding; and space radiation.

Benton, E. V.↗
NASA NTRS1996

Isopycnic Phases and Structures in H2O/CO2/Ethoxylated Alcohol Surfactant Mixtures

Ternary mixtures of H2O and CO2 with ethoxylated alcohol (C(i)E(j)) surfactants can form three coexisting liquid phases at conditions where two of the phases have the same density (isopycnic phases). Isopycnic phase behavior has been observed for mixtures containing the surfactants C8E5, C10E6, and C12E6, but not for those mixtures containing either C4E1 or CgE3. Pressure-temperature (PT) projections for this isopycnic three-phase equilibrium were determined for H2O/CO2/C8E5 and H2O/CO2/C10E6 mixtures at temperatures from approximately 25 to 33 C and pressures between 90 and 350 bar. As a preliminary to measuring the microstructure in isopycnic three component mixtures, phase behavior and small angle neutron scattering (SANS) experiments were performed on mixtures of D2O/CO2/ n-hexaethyleneglycol monododecyl ether (C12E6) as a function of temperature (25-31 C), pressure (63.1-90.7 bar), and CO2 composition (0-3.9 wt%). Parameters extracted from model fits of the SANS spectra indicate that, while micellar structure remains essentially unchanged, critical concentration fluctuations increase as the phase boundary and plait point are approached.

Paulaitis, Michael E.↗
DOE OSTI2021

Direct determination of the zero-field splitting for the Fe 3+ ion in a synthetic polymorph of NaMgFe(C 2 O 4 ) 3 ·9H 2 O: A natural metal-organic framework

Here we employed inelastic neutron scattering (INS), specific heat, and magnetization analysis to study the magnetism in a synthetic polymorph of the quasi-two-dimensional natural metal-organic framework material, stepanovite NaMgFe(C 2 O 4 ) 3 ∙9H 2 O. No long-range magnetic order can be observed down to 0.5 K. The INS spectra show two dispersionless excitations at energy transfer 0.028(1) and 0.050(1) meV at base temperature, which are derived from the magnetic transitions between zero-field splitting (ZFS) of S = 5/2 ground state multiplets of Fe 3+ ion. Further analysis of the INS results shows that the Fe 3+ ion has an easy-axis anisotropy with axial ZFS parameter D = –0.0128(5) meV and rhombic parameter E = 0.0014(5) meV. The upward behavior at zero field and Schottky-like peak under magnetic field of the low-temperature magnetic specific heat further support the INS results. Our results clearly reveal the magnetic ground and excited state of this stepanovite polymorph.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1989

Comptonization of thermal photons by relativistic electron beams

This paper presents a numerical calculation of gamma-ray emission produced by Compton scattering of relativistic electron beams on background thermal radiation, which includes spatial dependence of electron energy losses and cyclotron resonance scattering in a strong magnetic field. In the first version, the scattering is described by the fully relativistic Klein-Nishina cross section, but the magnetic field is neglected. In the second version, the scattering is described by the magnetic resonant cross section in the Thomson limit. It is found that when the magnetic field is not included, electron energy losses are important only at higher neutron star surface temperatures (T about 3,000,000 K). In the presence of a strong magnetic field, (10 to the 12th G), resonant scattering greatly increases electron energy losses, making scattering very efficient even at lower surface temperatures. Resulting photon and electron spectra for both cases ae discussed in relation to models for pulsar X-ray and gamma-ray emission.

Daugherty, Joseph K.↗
NASA NTRS1993

Status of LDEF ionizing radiation measurements and analysis

At this symposium significant new data and analyses were reported in cosmic ray research, radiation dosimetry, induced radioactivity, and radiation environment modeling. Measurements of induced radioactivity and absorbed dose are nearly complete, but much analysis and modeling remains. Measurements and analyses of passive nuclear track detectors (PNTD), used to derive the cosmic ray composition and spectra, and linear energy transfer (LET) spectra, are only a few percent complete, but important results have already emerged. As one might expect at this stage of the research, some of the new information has produced questions rather than answers. Low-energy heavy nuclei detected by two experiments are not compatible with known solar or cosmic components. Various data sets on absorbed dose are not consistent, and a new trapped proton environment model does not match the absorbed dose data. A search for cosmogenic nuclei other than Be-7 on Long Duration Exposure Facility (LDEF) surfaces has produced an unexpected result, and some activation data relating to neutrons is not yet understood. Most of these issues will be resolved by the analysis of further experiment data, calibrations, or the application of the large LDEF data set that offers alternate data or analysis techniques bearing on the same problem. The scope of the papers at this symposium defy a compact technical summary. I have attempted to group the new information that I noted into the following groups: induced radioactivity; absorbed dose measurements; LET spectra and heavy ion dosimetry; environment modeling and three dimensional shielding effects; cosmogenic nuclei; and cosmic rays and other heavy ions. The papers generally are expository and have excellent illustrations, and I refer to their figures rather than reproduce them here. The general program and objectives of ionizing radiation measurements and analyses on LDEF has been described previously.

Parnell, Thomas A.↗
DOE OSTI2022

Phonons and phase symmetries in bulk CrCl 3 from scattering measurements and theory

Phonon-derived behaviors are important indicators of novel phenomena in transition metal trihalides, including spin liquid behavior, two-dimensional magnetism, and spin-lattice coupling. However, phonons and their dependence on spin structure and excitations have not been adequately explored. In this work, we probe and critically examine the vibrational properties of the prototype ferromagnetic honeycomb lattice material CrCl 3 using inelastic neutron scattering and density functional theory. We demonstrate that magnetic and van der Waals interactions are essential to describing the structure and phonons in CrCl 3 ; however, the specific spin configuration is unimportant. Further, this provides context for understanding thermal transport measurements as governed by dynamical spin-lattice couplings. More importantly, we introduce an efficient dynamic method that exploits translational symmetries in large conventional unit cells that generates insights into phonon dispersions, interactions, and measured spectra in terms of quantum phase interference conditions. This work opens new avenues for understanding phonons in layered magnets and more generally in conventional cell geometries of a variety of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Production of Very Light Elements and Strontium in the Early Ejecta of Neutron Star Mergers

Abstract We study the production of very light elements ( Z < 20) in the dynamical and spiral-wave wind ejecta of binary neutron star mergers by combining detailed nucleosynthesis calculations with the outcome of numerical relativity merger simulations. All our models are targeted to GW170817 and include neutrino radiation. We explore different finite-temperature, composition-dependent nuclear equations of state, and binary mass ratios, and find that hydrogen and helium are the most abundant light elements. For both elements, the decay of free neutrons is the driving nuclear reaction. In particular, ∼0.5–2 × 10 −6 M ⊙ of hydrogen are produced in the fast expanding tail of the dynamical ejecta, while ∼1.5–11 × 10 −6 M ⊙ of helium are synthesized in the bulk of the dynamical ejecta, usually in association with heavy r -process elements. By computing synthetic spectra, we find that the possibility of detecting hydrogen and helium features in kilonova spectra is very unlikely for fiducial masses and luminosities, even when including nonlocal thermodynamic equilibrium effects. The latter could be crucial to observe helium lines a few days after merger for faint kilonovae or for luminous kilonovae ejecting large masses of helium. Finally, we compute the amount of strontium synthesized in the dynamical and spiral-wave wind ejecta, and find that it is consistent with (or even larger than, in the case of a long-lived remnant) the one required to explain early spectral features in the kilonova of GW170817.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Thermal neutron scattering measurements and modeling of yttrium-hydrides for high temperature moderator applications

In this work, thermal neutron scattering measurements of yttrium hydride from 5 to 1,200 K were conducted to determine the change in inelastic scattering as a function of temperature and to probe for anharmonic effects. Additionally, measurements on samples of YH x from x = 1.62 to 1.90 were done to determine the effects of varying hydrogen concentration on the inelastic spectra. Changes in temperature affected the inelastic spectra in unanticipated ways, indicating that there are anharmonic effects, whereas hydrogen concentration did not significantly affect the inelastic spectra. These measurements were compared against the ENDF/B-VIII.0 thermal scattering files of YH 2 , as well as new thermal scattering files created by using the stochastic temperature-dependent effective potential (s-TDEP). Both libraries were found to be in good agreement with the experimental data at lower temperatures. At higher temperatures, the s-TDEP method is better at predicting the experimentally observed softening of phonon modes in acoustic and optical regions.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Shot noise cross-correlation functions and cross spectra - Implications for models of QPO X-ray sources

The cross-correlation functions (CCFs) and cross spectra expected for quasi-periodic oscillation (QPO) shot noise models are calculated under various assumptions, and the results are compared to observations. Effects due to possible coherence of the QPO oscillations are included. General formulas for the cross spectrum, the cross-phase spectrum, and the time-delay spectrum for QPO shot models are calculated and discussed. It is shown that the CCFs, cross spectra, and power spectra observed for Cyg X-e2 imply that the spectrum of the shots evolves with time, with important implications for the interpretation of these functions as well as of observed average energy spectra. The possible origins for the observed hard lags are discussed, and some physical difficulties for the Comptonization model are described. Classes of physical models for QPO sources are briefly addressed, and it is concluded that models involving shot formation at the surface of neutron stars are favored by observation.

Shibazaki, N.↗
NASA NTRS2017

Measuring Surface Bulk Elemental Composition on Venus

The extreme surface environment (462 C, 93 bars pressure) of Venus makes subsurface measurements of its bulk elemental composition extremely challenging. Instruments landed on the surface of Venus must be enclosed in a pressure vessel. The high surface temperatures also require a thermal control system to keep the instrumentation temperatures within their operational range for as long as possible. Since Venus surface probes can currently operate for only a few hours, it is crucial that the lander instrumentation be able to make statistically significant measurements in a short time. An instrument is described that can achieve such a measurement over a volume of thousands of cubic centimeters of material by using high energy penetrating neutron and gamma radiation. The instrument consists of a Pulsed Neutron Generator (PNG) and a Gamma-Ray Spectrometer (GRS). The PNG emits isotropic pulses of 14.1 MeV neutrons that penetrate the pressure vessel walls, the dense atmosphere and the surface rock. The neutrons induce nuclear reactions in the rock to produce gamma rays with energies specific to the element and nuclear process involved. Thus the energies of the detected gamma rays identify the elements present and their intensities provide the abundance of each element. The GRS spectra are analyzed to determine the Venus elemental composition from the spectral signature of individual major, minor, and trace radioactive elements. As a test of such an instrument, a Schlumberger Litho Scanner oil well logging tool was used in a series of experiments at NASA's Goddard Space Flight Center. The Litho Scanner tool was mounted above large (1.8 m x 1.8 m x.9 m) granite and basalt monuments and made a series of one-hour elemental composition measurements in a planar geometry more similar to a planetary lander measurement. Initial analysis of the results shows good agreement with target elemental assays

Venus↗
DOE OSTI2022

Single-shot measurements of pulse-front tilt in intense ps laser pulses and its effect on accelerated electron and ion beam characteristics (invited)

Here we report recent single-shot spatiotemporal measurements of laser pulses, including pulse-front tilt (PFT) and spatial chirp, taken at the Compact Multipulse Terawatt laser at the Jupiter Laser Facility in Livermore, CA. STRIPED FISH, a device that measures the complete 3D electric field of fs to ps laser pulses on a single shot, was adapted to near infrared for these measurements. We present the design of the instrument used for these experiments, the on-shot measurements of systematic high-order PFT, and shot-to-shot variations in the measurements of spatiotemporal couplings. Finally, we simulate the effect of PFT in target normal sheath acceleration experiments. These simulations showed that pulse front tilt can steer hot electrons, shape the distribution of the accelerating sheath field, and increase the variability of cutoff energy in the resulting proton spectra. While these effects may be detrimental to experimental accuracy if the pulse front tilt is left unmeasured, hot electron steering shows promise for precision manipulation of the particle source for a range of applications, including irradiation of secondary targets for opacity measurements, radiography, or neutron generation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

A target for production of radioxenons

A liquid cesium target has been developed which permits the production and identification of the neutron deficient isotopes of xenon. The thick target yields of Xe-127 and Xe-129 m were measured for proton energies between 28 and 40 MeV. Production of Xe-129 m, as indicated by the presence of a 196 keV line in the gamma ray spectra, occurred at all proton energies; Xe-127 was produced at proton energies above 33 MeV. Both accumulated on the target with the same time constant, and the cross sections were comparable in magnitude. The radioxenons were removed from the target by a stream of carrier gas so that chemical separation was unnecessary.

Blue, J. W.↗
NASA NTRS1989

Cyclotron line features from neutron star atmospheres

Cyclotron line features from the polar cap plasmas of accreting magnetized neutron stars are modeled. The polar cap environment is modeled by a homogeneous isothermal plane-parallel slab threaded by a uniform superstrong magnetic field oriented orthogonal to the slab. Two physical cyclotron photon source functions are used. For conventional stopping depths, the emergent line spectra are fairly independent of the source functions. For hot atmospheres the details of the line transfer using relativistic kinematics differ substantially from those using nonrelativistic kinematics. Aside from finite recoil, both a finite natural linewidth and conventional stopping depths suppress the escape of photons blueward of line center and potential line features tend to be smeared out into the low-energy continuum. The formation of a line features is most favorable in low-field high-temperature atmospheres where cyclotron photon production is confined to a layer of small column density.

Wang, John C. L.↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Mars: Radar, Gamma Ray Spectrometer, and Cratering Mineralogy

The session "Mars: Radar, Gamma Ray Spectrometer, and Cratering Mineralogy" contained the following reports:The Dielectric Properties of Martian Soil Simulant JSC Mars-1 in the Range from 20Hz to 10kHz; Eastern Sahara Geology from Orbital Radar: Potential Analog to Mars On the Dielectric Properties of the Martian-like Surface Sediments; Radar Observations of Recent Mars Landing Sites; Sounding of Subsurface Water Through Conductive Media in Mars Analog Environments Using Transient Electromagnetics and Low Frequency Ground-penetrating Radar; Burial Depth of the Reservoirs of Hydrogen at the Equatorial Latitudes on Mars; Elemental Composition Variations for Large Dusty and Rocky Regions on Mars Using Gamma-Ray Data from the Mars Odyssey Gamma-Ray Spectrometer; The Distribution of Non-Volatile Elements on Mars: Mars Odyssey GRS Results; Using Mars Odyssey GRS Data to Assess Models for the Bulk Composition of Mars; Mars: The Terra Arabia Low Epithermal Neutron Flux Anomaly; The Isidis Basin of Mars: New Results from MOLA, MOC, and THEMIS; Remote Sensing of the Haughton Impact Structure (HIS): A Terrestrial Proof of Concept for Using the Remote Sensing of Martian Craters as a Probe of Subsurface Composition;and Thermal Emission Spectra of Impact Glass and Shocked Deccan Basalt from Lonar Crater, India and Implications for Remote Sensing of Mars.

Source record↗