Search NASA⌕ Search

SEARCH · Search NASA

Results for “Neutron Probe”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Thermonuclear Burning as a Probe of Neutron Star

Thermonuclear fusion is a fundamental process taking place in the matter transferred onto neutron stars in accreting binary systems. The heat deposited by nuclear reactions becomes readily visible in the X-ray band when the burning is either unstable or marginally stable, and results in the rich phenomenology of X-ray bursts, superbursts, and mHz quasiperiodic oscillations. Fast X-ray timing observations with NASA's Rossi X-ray Timing Explorer (RXTE) over the past decade have revealed a wealth of new phenomena associated with thermonuclear burning on neutron stars, including the discovery of nuclear powered pulsations during X-ray bursts and superbursts. I will briefly review our current observational and theoretical understanding of these new phenomena, with an emphasis on recent findings, and discuss what they are telling us about the structure of neutron stars.

Strohmayer, Tod↗
DOE OSTI2016

Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet

Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. While their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting due to the emergence of fundamentally new excitations such as Majorana Fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. We report these here for a ruthenium-based material α-RuCl 3 , continuing a major search (so far concentrated on iridium materials inimical to neutron probes) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisite strong spin-orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly 2D nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl 3 as prime candidate for realization of fractionalized Kitaev physics.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Lunar neutron capture as a tracer for regolith dynamics

The Apollo 17 Lunar Neutron Probe Experiment measured both the boron-10 neutron capture rate and the uranium-235 neutron-induced fission rate as a function of depth. Cd absorption gave a measure of the neutron energy spectrum. Comparisons of the results are made with theory, and good agreement is obtained for the magnitudes and depth dependences of the capture rates. While the low-energy neutron spectrum at depth agrees with theory, the spectrum near the peak of the flux profile is harder than predicted. In light of these results, several alternatives for interpreting the magnitude and uniformity of the neutron capture data from lunar surface soil samples are outlined. While none of the alternatives can be unquestionably defended or discarded, a surface layer mixing model is discussed in detail.

Burnett, D. S.↗
DOE OSTI2015

A compact broadband ion beam focusing device based on laser-driven megagauss thermoelectric magnetic fields

Ultra-intense lasers can nowadays routinely accelerate kiloampere ion beams. These unique sources of particle beams could impact many societal (e.g., proton-therapy or fuel recycling) and fundamental (e.g., neutron probing) domains. However, this requires overcoming the beam angular divergence at the source. This has been attempted, either with large-scale conventional setups or with compact plasma techniques that however have the restriction of short (<1 mm) focusing distances or a chromatic behavior. Here, we show that exploiting laser-triggered, long-lasting (>50 ps), thermoelectric multi-megagauss surface magnetic (B)-fields, compact capturing, and focusing of a diverging laser-driven multi-MeV ion beam can be achieved over a wide range of ion energies in the limit of a 5° acceptance angle.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Field Soil Water Retention of the Prototype Hanford Barrier and Its Variability with Space and Time

Engineered surface barriers (or covers) are used to isolate underlying contaminants from water, plants, animals, and humans. To understand the flow processes within a barrier and the barrier's ability to store and release water, the field hydraulic properties of the barrier need to be known. A multiyear test of the evapotranspiration (ET) barrier at the US Department of Energy's Hanford Site in the southeast of the state of Washington has yielded in situ soil water content and pressure data from multiple locations for a 9‐yr period, offering the opportunity to estimate soil water retention properties at different locations and times. The upper 2‐m layer of the ET barrier is a silt loam, and the top 1 m also contains 15% (w/w) pea gravel. Within this layer, valid monitoring data from 1995 to 2003 for four depths at 12 monitoring stations were used to determine the field water retention of the silt loam, with and without gravel. The data covered a wide range of wetness, from near saturation to the permanent wilting point, and each retention curve contained 51 to 96 data points. The data were described well with the commonly used van Genuchten water retention model. It was found that the spatial variation of the saturated and residual water content and the pore size distribution parameter was relatively small, while that of the van Genuchten α was relatively large. The effects of spatial variability of the retention properties appeared to be larger than the combined effects of added pea gravel and plant roots on the properties. Neither the primary wetting process in the winter season nor the drying process in the summer season nor time had a detectable effect on the water retention of the silt loam barrier.

Zhang, Z. Fred↗
NASA NTRS1978

Gamma-ray lines from neutron stars as probes of fundamental physics

The detection of gamma-ray lines produced at the surface of neutron stars will serve to test both the strong and gravitational interactions under conditions unavailable in terrestrial laboratories. Observation of a single redshifted gamma-ray line, combined with an estimate of the mass of the star will serve as a strong constraint on allowable equations of state of matter at supernuclear densities. Detection of two redshifted lines arising from different physical processes at the neutron star surface can provide a test of the strong principle of equivalence. Expected fluxes of nuclear gamma-ray lines from accreting neutron stars were calculated, including threshold, radiative transfer and redshift effects. The most promising probes of neutron star structure are the deuterium formation line and the positron annihilation line. Detection of sharp redshifted gamma-ray lines from X-ray sources such as Cyg X-1 would argue strongly in favor of a neutron star rather than black hole identification for the object.

Brecher, K.↗
DOE OSTI2026

Multi-modal dynamic radiography using short-pulse laser-generated probe beams

Radiography is an important tool for the interrogation of dynamic experiments in the fields of dynamic properties of materials, and in condensed matter, high explosive, and high-energy-density physics. Multi-modal radiography advances the hypothesis that combining the information delivered by multiple radiographic modalities can lead to more constrained (improved) “reconstruction” of the scene than can be obtained from a single probe. We identify four modalities: multi-probe, time sequence, multi-view, and multi-messenger. Multi-probe radiography is a promising candidate for a next-generation dynamic radiographic facility. High-energy X-rays are the most frequently used probe for dynamic radiography, although recent developments show the utility of proton (pRad), electron (eRad), and neutron probe beams. Because each probing species interacts with material in the radiographic scene through quantitatively different mechanisms, each returns independent information about the scene, which can add extra constraints to the reconstruction process. How to conduct detailed, quantitative “co-analysis” of multiple data streams remains an area of active research. Multi-beam, short-pulse, laser-generated probes offer sufficient dose, an appropriate spectrum, and appropriate spatio-temporal resolution to produce high-quality dynamic radiographs. This paper reports on technology development to advance the state of the art of multi-modal/multi-probe radiography and the pursuit of both deterministic and inferential (AI/ML assisted) co-analysis methodologies to produce more constrained reconstructions from multi-modal data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Weak-coupling theory of neutron scattering as a probe of altermagnetism

Inelastic neutron scattering provides a powerful probe of the magnetic excitations of quantum magnets. Altermagnets have recently emerged as a new class of magnets with vanishing net magnetization characteristic of antiferromagnets and with a spin-split electronic structure typical of ferromagnets. Here we introduce a minimal Hubbard model with two-sublattice orthorhombic anisotropy as a framework to study altermagnetism. Using unrestricted Hartree-Fock calculations, we find an altermagnetic state for this model that evolves from a metallic state to an insulating state with increasing Hubbard-U Coulomb repulsion. We then examine the inelastic neutron scattering response in these states using random-phase approximation calculations of the dynamic spin susceptibility χ"(q,ω). We find that the magnetic excitation spectrum depends on its chirality for q along certain directions in reciprocal space, an observation that may be used in inelastic neutron scattering experiments as a probe of altermagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1975

Measurement of the lunar neutron density profile

Relatively small discrepancies between Apollo 17 lunar neutron probe experiment (LNPE) data and theoretical calculations by Lingenfelter, Canfield, and Hampel in the effect of Cd absorption on the neutron density, and in the relative Sm-149 to Gd-157 capture rates reported previously, imply that the true lunar Gd-157 capture rate is about one-half of that derived theoretically.

Woolum, D. S.↗
NASA NTRS2008

"Magnetar Hyper-Flares: Whole Lotta Shakin' Goin' on"

The giant flares produced by highly magnetized neutron stars, "magnetars," are the brightest sources of high energy radiation outside our solar system. High frequency oscillations have been discovered during portions of the two most recently observed giant flares which may represent the first detection of global oscillation modes of neutron stars. I will give an observational and theoretical overview of these oscillations and describe how they might allow us to probe neutron star interiors and dense matter physics.

Strohmayer, Tod↗
NASA NTRS2009

Fast X-Ray Oscillations during Magnetar Flares

The giant flares produced by highly magnetized neutron stars, "magnetars," are the brightest sources of high energy radiation outside our solar system. High frequency oscillations have been discovered during portions of the two most recently observed giant flares which may represent the first detection of global oscillation modes of neutron stars. I will give an observational and theoretical overview of these oscillations and describe how they might allow us to probe neutron star interiors and dense matter physics.

Strohmayer Tod E.↗
NASA NTRS1974

Measurement of the lunar neutron density profile

An in situ measurement of the lunar neutron density from 20 to 400 g/sq cm depth between the lunar surface was made by the Apollo 17 Lunar Neutron Probe Experiment using particle tracks produced by the B10(n, alpha)Li7 reaction. Both the absolute magnitude and depth profile of the neutron density are in good agreement with past theoretical calculations. The effect of cadmium absorption on the neutron density and in the relative Sm149 to Gd157 capture rates obtained experimentally implies that the true lunar Gd157 capture rate is about one half of that calculated theoretically.

Woolum, D. S.↗
NASA NTRS2007

Evidence for a Broad Relativistic Iron Line from the Neutron Star LMXB Ser X-1

We report on an analysis of XMM-Newton data from the neutron star low mass X-ray binary (LMXB) Serpens X-1 (Ser X-1). Spectral analysis of EPIC PN data indicates that the previously known broad iron Ka emission line in this source has a significantly skewed structure with a moderately extended red wing. The asymmetric shape of the line is well described with the laor and diskline models in XSPEC, which strongly supports an inner accretion disk origin of the line. To our knowledge this is the first strong evidence for a relativistic line in a neutron star LMXB. This finding suggests that the broad lines seen in other neutron star LMXBs likely originate from the inner disk as well. Detailed study of such lines opens up a new way to probe neutron star parameters and their strong gravitational fields. The laor model describes the line from Ser X-1 somewhat better than diskline, and suggests that the inner accretion disk radius is less than 6GM/c(exp 2). This is consistent with the weak magnetic fields of LMXBs, and may point towards a high compactness and rapid spin of the neutron star. Finally, the inferred source inclination angle in the approximate range 50-60 deg is consistent with the lack of dipping from Ser X-1.

Bhattacharyya, Sudip↗
NASA NTRS2007

Fast X-ray Oscillations during Magnetar Flares

The giant flares produced by highly magnetized neutron stars, "magnetars," are the brightest sources of high energy radiation outside our solar system. Serendipitous observations with NASA's Rossi X-ray Timing Explorer (RXTE) of the two most recent flares resulted in the discovery of high frequency oscillations in their X-ray fluxes. The frequencies of these oscillations range from approx. 20 Hz to as high as 1800 Hz, and may represent the first detection of global oscillation modes of neutron stars. Here I will present an observational and theoretical overview of these oscillations and discuss how they might allow us to probe neutron star interiors and dense matter physics.

Strohmayer, Tod E.↗
NASA NTRS2004

Future Probes of the Neutron Star Equation of State Using X-ray Bursts

Observations with NASA s Rossi X-ray Timing Explorer (RXTE) have resulted in the discovery of fast (200 - 600 Hz), coherent X-ray intensity oscillations (hereafter, %urstoscillations ) during thermonuclear X-ray bursts from 12 low mass X-ray binaries (LMXBs). Although many of their detailed properties remain to be fully understood, it is now beyond doubt that these oscillations result from spin modulation of the thermonuclear burst flux from the neutron star surface. Among the new timing phenomena revealed by RXTE the burst oscillations are perhaps the best understood, in the sense that many of their properties can be explained in the framework of this relatively simple model. Because of this, detailed modelling of burst oscillations can be an extremely powerful probe of neutron star structure, and thus the equation of state (EOS) of supra-nuclear density matter. Both the compactness parameter beta = GM/c(sup 2)R, and the surface velocity, nu(sub rot) = Omega(sub spin)R, are encoded in the energy-dependent amplitude and shape of the modulation pulses. The new discoveries have spurred much new theoretical work on thermonuclear burning and propagation on neutron stars, so that in the near future it is not unreasonable to think that detailed physical models of the time dependent flux from burning neutron stars will be available for comparison with the observed pulse profiles from a future, large collecting area X-ray timing observatory. In addition, recent high resolution burst spectroscopy with XMM/Newton suggests the presence of redshifted absorption lines from the neutron star surface during bursts. This leads to the possibility of using large area, high spectral resolution measurements of X-ray bursts as a precise probe of neutron star structure. In this work I will explore the precision with which constraints on neutron star structure, and hence the dense matter EOS, can be made with the implementation of such programs.

Strohmayer, Tod E.↗