Search NASA⌕ Search

SEARCH · Search NASA

Results for “Neutron emission”

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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Neutron Radiography and Computed Tomography of Biological Systems at the Oak Ridge National Laboratory's High Flux Isotope Reactor

Neutrons have historically been used for a broad range of biological applications employing techniques such as small-angle neutron scattering, neutron spin echo, diffraction, and inelastic scattering. Unlike neutron scattering techniques that obtain information in reciprocal space, attenuation-based neutron imaging measures a signal in real space that is resolved on the order of tens of micrometers. The principle of neutron imaging follows the Beer-Lambert law and is based on the measurement of the bulk neutron attenuation through a sample. Greater attenuation is exhibited by some light elements (most notably, hydrogen), which are major components of biological samples. Contrast agents such as deuterium, gadolinium, or lithium compounds can be used to enhance contrast in a similar fashion as it is done in medical imaging, including techniques such as optical imaging, magnetic resonance imaging, X-ray, and positron emission tomography. For biological systems, neutron radiography and computed tomography have increasingly been used to investigate the complexity of the underground plant root network, its interaction with soils, and the dynamics of water flux in situ. Moreover, efforts to understand contrast details in animal samples, such as soft tissues and bones, have been explored. This manuscript focuses on the advances in neutron bioimaging such as sample preparation, instrumentation, data acquisition strategy, and data analysis using the High Flux Isotope Reactor CG-1D neutron imaging beamline. The aforementioned capabilities will be illustrated using a selection of examples in plant physiology (herbaceous plant/root/soil system) and biomedical applications (rat femur and mouse lung).

Bilheux, Hassina↗
NASA NTRS1979

X-ray pulsar spectroscopy - Observational prospects

Three experimental concepts have been suggested to advance the study of X-ray pulsar spectroscopy. They are: (1) a higher bit rate for pulse phase spectroscopy; (2) an emphasis on the 10 keV 'pulsar surface' emission, and (3) an improved resolution to understand the nature of broadened iron lines in pulsars. It is shown that for conventional X-ray spectroscopy at least 5 KB/s are needed to substantially improve pulse phase spectroscopy; the broadened iron line emission in the pulsar spectra will require improved spectral resolution at 6.7 keV to discriminate among the models for this emission. It is concluded that this work will elucidate the physics of neutron star surface and circumstellar X-ray emission.

Pravdo, S. H.↗
NASA NTRS1995

Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment

We employ an approximate treatment of dissipative hydrodynamics in three dimensions to study the coalescence of binary neutron stars driven by the emission of gravitational waves. The stars are modeled as compressible ellipsoids obeying a polytropic equation of state; all internal fluid velocities are assumed to be linear functions of the coordinates. The hydrodynamics equations then reduce to a set of coupled ordinary differential equations for the evolution of the principal axes of the ellipsoids, the internal velocity parameters, and the binary orbital parameters. Gravitational radiation reaction and viscous dissipation are both incorporated. We set up exact initial binary equilibrium configurations and follow the transition from the quasi-static, secular decay of the orbit at large separation to the rapid dynamical evolution of the configurations just prior to contact. A hydrodynamical instability resulting from tidal interactions significantly accelerates the coalescence at small separation, leading to appreciable radial infall velocity and tidal lag angles near contact. This behavior is reflected in the gravitational waveforms and may be observable by gravitational wave detectors under construction. In cases where the neutron stars have spins which are not aligned with the orbital angular momentum, the spin-induced quadrupole moment can lead to precession of the orbital plane and therefore modulation of the gravitational wave amplitude even at large orbital radius. However, the amplitude of the modulation is small for typical neutron star binaries with spins much smaller than the orbital angular momentum.

Lai, Dong↗
DOE OSTI2025

C 12 ( n , n 1 ′ γ ) partial γ -ray cross section measured using the GENESIS array

Improved neutron inelastic scattering cross sections have repeatedly been identified as a top priority nuclear data need, important for basic science and a range of applications in nuclear energy, stockpile stewardship, and proliferation detection. For the C 12 ( n , n ′ γ ) reaction in particular, recent measurements have unveiled some structural discrepancies, demonstrating incongruities among themselves and in relation to the ENDF/B-VIII.0 nuclear data evaluation. To help resolve these disagreements, a measurement was performed at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory using a broad-spectrum neutron beam and a 99.8% pure natural carbon target. The Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) was employed to measure energy-differential γ -ray emission spectra as a function of incident neutron energy in the energy range of 5.5 to 16.7 MeV. The C 12 partial γ -ray cross sections were extracted at 63 ∘ , 122 . 5 ∘ , and 150 ∘ with respect to the incoming neutron beam and integrated using angular distribution data available in the literature. The data show agreement with a recent literature measurement and evaluation from 11 to 15 MeV, but indicate a larger cross section for incident neutron energies between 5.5 and 8.5 MeV. The measured relative angular distributions are also reported and were found to agree with evaluation. Published by the American Physical Society 2025

Gordon, J. M. (ORCID:0009000789886897)↗
NASA NTRS1977

The effect of vacuum birefringence on the polarization of X-ray binaries and pulsars

In a strong magnetic field the vacuum becomes birefringent. This effect is especially important for pulsars at X-ray wavelengths. Any polarized X-ray emission from the surface of a magnetic neutron star becomes depolarized as it propagates through the magnetic field. The soft X-ray emission from AM Her, believed to be a magnetic white dwarf, may show about one radian of phase retardation. In this case, circular polarization of the X-ray flux would be a characteristic signature of vacuum birefringence.

Novick, R.↗
NASA NTRS2014

The Neutron Star Zoo

Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not clear how effective it is or on what timescale a buried field might re-emerge. One piece of evidence in favor of accretion-driven field reduction is the fact that NSs in LMXBs, which are older systems (> 108 yr), have mostly low fields and NSs in HMXBs, which are younger systems (107 − 108 yr), have higher fields. This may be an indication that accretion-driven field reduction or decay has not had enough time to operate in HMXBs but has in LMXBs. However, there does not seem to be any evidence of decaying fields in either the LMXB or HMXB populations; e.g. smaller magnetic fields in older systems. On the other hand, CCOs are very young so if they acquired their low fields through mass fallback accretion, the field submergence would have had to operate on much faster timescales than it apparently does in LMXBs. But as we continue to find new species in the NS zoo, one of these may someday be the "Rosetta Stone" that will give us the clues for solving these puzzles.

Zoo↗
NASA NTRS1987

Probable detection of solar neutrons by ground-level neutron monitors during STIP interval 16

The third solar neutron event detected by Earth-orbiting spacecraft was observed during STIP Interval XVI. The solar flare beginning at 2356 UT on 24 April l984 produced a variety of emissions including gamma rays and solar neutrons. The neutrons were observed by the SMM satellite and the neutron-decay protons were observed on the ISEE-3 spacecraft. Between 0000 and 0010 UT on 25 April an increase of 0.7 and 1.7 percent was recorded by neutron monitors at Tokyo (Itabashi) and Morioka, Japan. These stations were located about 42 degrees from the sub-solar point, and consequently, these is approximately 1400 grams of atmosphere between the incident neutrons at the top of the atmosphere and their detection on the Earth's surface. Nevertheless, the time coincidence of a small increase in the total counting rate of two independent neutron monitors indicates the presence of solar neutrons with energies greater than 400 MeV at the top of the Earth's atmosphere. The small increases in the counting rate emphasize the difficulty in identifying similar events using historical neutron monitor data.

Shea, M. A.↗
NASA NTRS1985

Time extended production of neutrons during a solar flare

The most energetic neutral emissions expected from solar flares are gamma rays (10 MeV) from relativistic primary and secondary electron bremsstrahlung,from approx 0 meson decay, and from neutrons ( 50 MeV). Bremsstrahlung photon energies extend to that of the highest energy electron present, but the shape of the pi sup 0 gamma ray spectrum, peaking at 69 MeV, does not depend strongly on the proton spectrum above threshold, which is approx. 292 MeV for meson production on protons. The highest energy neutrons observed indicate directly the highest energy ions which interact at the Sun, and the presence or absence of anergy cutoff in the acceleration process. The high-energy proton spectrum shape can be determined from the neutron spectrum.

Chupp, E. L.↗
DOE OSTI2025

Ohm’s Law, the Reconnection Rate, and Energy Conversion in Collisionless Magnetic Reconnection

Magnetic reconnection is a ubiquitous plasma process that transforms magnetic energy into particle energy during eruptive events throughout the universe. Reconnection not only converts energy during solar flares and geomagnetic substorms that drive space weather near Earth, but it may also play critical roles in the high energy emissions from the magnetospheres of neutron stars and black holes. In this review article, we focus on collisionless plasmas that are most relevant to reconnection in many space and astrophysical plasmas. Guided by first-principles kinetic simulations and spaceborne in-situ observations, we highlight the most recent progress in understanding this fundamental plasma process. We start by discussing the non-ideal electric field in the generalized Ohm’s law that breaks the frozen-in flux condition in ideal magnetohydrodynamics and allows magnetic reconnection to occur. We point out that this same reconnection electric field also plays an important role in sustaining the current and pressure in the current sheet and then discuss the determination of its magnitude (i.e., the reconnection rate), based on force balance and energy conservation. This approach to determining the reconnection rate is applied to kinetic current sheets with a wide variety of magnetic geometries, parameters, and background conditions. We also briefly review the key diagnostics and modeling of energy conversion around the reconnection diffusion region, seeking insights from recently developed theories. Finally, future prospects and open questions are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Dynamics of a relativistic jet through magnetized media

The merger of two neutron stars (NSs) produces the emission of gravitational waves, the formation of a compact object surrounded by a dense and magnetized environment. If the binary undergoes delayed collapse a collimated and relativistic jet, which will eventually produce a short gamma-ray burst (SGRB), may be launched. The interaction of the jet with the environment has been shown to play a major role in shaping the structure of the outflow that eventually powers the gamma-ray emission. In this paper, we present a set of 2.5D RMHD simulations that follow the evolution of a relativistic non-magnetized jet through a medium with different magnetization levels, as produced after the merger of two NSs. We find that the predominant consequence of a magnetized ambient medium is that of suppressing instabilities within the jet and preventing the formation of a series of collimation shocks. One implication of this is that internal shocks lose efficiency, causing bursts with low-luminosity prompt emission. On the other hand, the jet-head velocity and the induced magnetization within the jet are fairly independent of the magnetization of the ambient medium. Future numerical studies with a larger domain are necessary to obtain light curves and spectra in order to better understand the role of magnetized media.

(magnetohydrodynamics) MHD↗
DOE OSTI2020

γ-ray measurements in fast-neutron-induced reactions on 203 Tl

Fast-neutron-induced reactions can be used to characterize reaction mechanisms, investigate nuclear structure, and impose constraints on nuclear models. Because of the difficulty in predicting such effects, experimental data are important to constrain models. Thallium isotopes located close to the doubly magic Pb 208 nucleus are important for comparison with shell-model calculations. Study the population of excited states in Tl 203 and lighter isotopes in such reactions. Our methods are as follows. γ -ray cross sections were measured. The data were taken by using the Germanium Array for Neutron-Induced Excitations spectrometer. The pulsed neutron source of the Los Alamos Neutron Science Center's Weapons Neutron Research facility provided neutrons in the energy range from 1 to 300 MeV. The time-of-flight technique was used to determine the incident neutron energies. Cross sections for emission of several γ rays in 20 reaction channels were determined. Candidates for the intruder 9 / 2 - state in Tl 203 , from the odd proton in the h 9 / 2 orbital, and the first 5 + states in Tl 202 , 204 , from admixture of configurations, were identified. The excitation energy of the candidate 9 / 2 - , π h 9 / 2 state is in good agreement with the theoretical prediction from a semi-empirical weak-coupling model and its half-life is in the range of tens of nanoseconds. The feeding of a previously known isomer in Tl 202 exhibits similarities with the feeding of other isomers in this mass region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Where, when, and why: Occurrence of fast-pairwise collective neutrino oscillation in three-dimensional core-collapse supernova models

Fast-pairwise collective neutrino oscillation represents a key uncertainty in the theory of core-collapse supernova (CCSN). Despite the potentially significant impact on CCSN dynamics, it is usually neglected in numerical models of CCSN because of the formidable technical difficulties of self-consistently incorporating this physics. In this paper, we investigate the prospects for the occurrence of fast flavor conversion by diagnosing electron neutrino lepton number (ELN) crossing in more than a dozen state-of-the-art three-dimensional CCSN models. ELN crossings provide a necessary condition for triggering flavor conversion. Although only zeroth and first angular moments are available from the simulations, our new method enables us to look into the angular distributions of neutrinos in momentum space and provide accurate insight into ELN crossings. Our analysis suggests that fast flavor conversion generally occurs in the postshock region of CCSNe, and that explosive models provide more favorable conditions for the flavor conversion than failed CCSNe. Here we also find that there are both common and progenitor-dependent characteristics. Classifying ELN crossings into two types, we analyze the generation mechanism of each case by scrutinizing the neutrino radiation field and matter interactions. We find key ingredients of CCSN dynamics driving the ELN crossings: proto-neutron star convection, asymmetric neutrino emission, neutrino absorptions, and scatterings. This study suggests that we need to accommodate fast flavor conversions in realistic CCSN models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Study of alpha-resonances in ¹¹B via the ⁷Li(⁷Li, t ) reaction

The near-threshold proton resonance in ¹¹B, recently identified and characterized through independent experi-ments, plays a crucial role in understanding the unexpectedly high decay branch observed in the β-delayed proton emission (β− p) from the neutron halo nucleus ¹¹Be. Critical to interpreting this process is the determination of whether or not this state has any significant α-decay width (rα). A coincidence measurement was conducted to study the alpha-transfer reaction ⁷Li(⁷Li, t ) ¹¹B∗ → ⁷Li +α employing the Super-Enge Split Pole Spectrograph coupled with a silicon detector at Florida State University. This experiment aimed to investigate the structure of α resonances in ¹¹B in the Eₑₓ = 9.0 MeV–14 MeV energy region. In particular, to explore and constrain the α-decay branch of the near-threshold proton resonance at Eₑₓ = 11.44 MeV. No significant α-decay strength was observed from this state. Additionally, the experimental results provided insights into the state at Eₑₓ = 12.55 MeV, previously proposed as the T = 3/2 isobaric analog state of the ¹¹Be ground state. The observed decay pattern, dominated by α + ⁷Li, suggests a strong T = 1/2 component, indicating the need for further experimental measurements.

Lopez-Saavedra, E.↗
DOE OSTI2023

Passive methods for spent fuel characterisation at the Finnish geological repository

Development of the Passive Gamma Emission Tomography (PGET) and Passive Neutron Albedo Reactivity (PNAR) methods in the context of the Finnish geological repository for spent nuclear fuel has shown that they provide, for BWR fuel assemblies, the comprehensive verification needed to meet the nuclear safeguards objectives of the repository. The principles of the PGET and PNAR methods and the design and operation of the respective instruments are presented. A few results from measurements at the spent fuel storage pools at the Finnish nuclear power plants are discussed. The directions of ongoing and future developments are indicated.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2020

Radiation Damage in Materials—Helium Effects

Despite its scarcity in terrestrial life, helium effects on microstructure evolution and thermo-mechanical properties can have a significant impact on the operation and lifetime of applications, including: advanced structural steels in fast fission reactors, plasma facing and structural materials in fusion devices, spallation neutron target designs, energetic alpha emissions in actinides, helium precipitation in tritium-containing materials, and nuclear waste materials. The small size of a helium atom combined with its near insolubility in almost every solid makes the helium–solid interaction extremely complex over multiple length and time scales. This Special Issue, “Radiation Damage in Materials—Helium Effects”, contains review articles and full-length papers on new irradiation material research activities and novel material ideas using experimental and/or modeling approaches. These studies elucidate the interactions of helium with various extreme environments and tailored nanostructures, as well as their impact on microstructural evolution and material properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nucleosynthesis of an 11.8 M ⊙ Supernova with 3D Simulation of the Inner Ejecta: Overall Yields and Implications for Short-lived Radionuclides in the Early Solar System

Based on a 3D supernova simulation of an 11.8 M ⊙ progenitor model with an initial solar composition, we study the nucleosynthesis using tracers covering the innermost 0.1 M ⊙ of the ejecta. These ejecta are mostly proton-rich and contribute significant amounts of 45 Sc and 64 Zn. The production of heavier isotopes is sensitive to the electron fraction and hence the neutrino emission from the proto-neutron star. The yields of these isotopes are rather uncertain due to the approximate neutrino transport used in the simulation. In order to obtain the total yields for the whole supernova, we combine the results from the tracers with those for the outer layers from a suitable 1D model. Using the yields of short-lived radionuclides (SLRs), we explore the possibility that an 11.8 M ⊙ supernova might have triggered the formation of the solar system and provided some of the SLRs measured in meteorites. In particular, we discuss two new scenarios that can account for at least the data on 41 Ca, 53 Mn, and 60 Fe without exceeding those on the other SLRs.

Astronomy & Astrophysics↗
NASA NTRS1976

Gamma-ray astronomy: Nuclear transition region

This monograph reviews the major theoretical and experimental efforts made during the past 12 years in gamma-ray astronomy over the energy range from 10 keV to about 100 MeV, where nuclear-transition lines are expected. Early attempts to detect celestial gamma rays are recounted, mechanisms of gamma-ray line and continuum production are examined, and formulas giving the various possible differential gamma-ray spectral shapes are provided. Predicted fluxes are discussed for solar gamma rays as well as for gamma emission from supernova remnants, supernovae, neutron stars, flare stars, the galactic core and disk, black holes, and diffuse sources. Gamma-ray interactions with matter are analyzed, particularly the photoelectric effect, Compton scattering from free electrons, and pair production in nuclear fields. Significant results are summarized for observations of gamma rays from the sun as well as from point and extended sources within and beyond the Galaxy, including diffuse fluxes and transient gamma-ray bursts. Factors pertaining to the design of gamma-ray astronomy experiments are considered, especially detector background limitations, gamma-ray production within instruments, and present-day detection methods.

Chupp, E. L.↗