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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

On the reconciliation of simultaneous microwave imaging and hard X-ray observations of a solar flare

Microwave imaging data for a small flare with simultaneous hard X-ray spectral observations are compared. The X-ray data suggest that the power-law index delta of the energy distribution of the radiating electrons is 5.3 (thick-target) which differs significantly from the estimate (delta = 1.4) from a homogeneous optically-thin gyrosynchrotron model which fits the radio observations well. In order to reconcile these results, a double power-law energy spectrum is investigated for the energetic electrons in the flare, as assumed by other authors: the power law is steep at low energies and much flatter at the higher energies which produce the bulk of the microwaves. The emission of soft photons by the flat tail strongly contributes to the observed hard X-ray range and would flatten the spectrum there. A thin-target model for the X-ray emission is also inconsistent with radio data. An inhomogenous gyrosychrotron model with a number of free parameters and containing an electron distribution given by the thick-target X-ray model could be made to fit the radio data.

Nitta, N.↗
NASA NTRS2006

MEMS-Based Force-Detected Nuclear Magnetic Resonance (FDNMR) Spectrometer

Nuclear Magnetic Resonance (NMR) spectroscopy allows assignment of molecular structure by acquiring the energy spectrum of nuclear spins in a molecule, and by interpreting the symmetry and positions of resonance lines in the spectrum. As such, NMR has become one of the most versatile and ubiquitous spectroscopic methods. Despite these tremendous successes, NMR experiments suffer from inherent low sensitivity due to the relatively low energy of photons in the radio frequency (rt) region of the electromagnetic spectrum. Here, we describe a high-resolution spectroscopy in samples with diameters in the micron range and below. We have reported design and fabrication of force-detected nuclear magnetic resonance (FDNMR).

force detected nuclear magnetic resonance (FDNMR)↗
NASA NTRS1985

An upper limit of muon flux of energies above 100 TeV determined from horizontal air showers observed at Akeno

Muon energy spectrum above 100 TeV was determined by observing the extensive air showers (EAS) from the horizontal direction (HAS). No definite muon originated shower of sizes above 100,000 and zenith angles above 60 deg was observed. The upper limits of HAS intensity is 5x10/12 m/2 s/1 sn/1 above 100,000. It is indicated that the upper limit of muon flux above 100 TeV is about 1.3x10/8 m/2 s/1 sr/1 and is in agreement with that expected from the primary spectrum with a knee assuming scaling in the fragmentation region and 40% protons in the primary beam. The critical energy at which muon flux from prompt processes take over that from the conventional process is higher than 100 Tev at horizontal direction.

Nagano, M.↗
NASA NTRS2006

Secondary Electron Emission and the Exploration of Space

The emission of secondary electrons from surfaces exposed to the space plasma and radiation environment is a process of great importance to space system engineering design and operations. A spacecraft will collect charge until it reaches an equilibrium potential gov,erned by the balance of incoming electron and ion currents from the space environment with outgoing secondary, backscattered, and photoelectron currents. Laboratory measurements of secondary electron yields are an important parameter for use in spacecraft charging analyses because the magnitude and sign of the equilibrium potential depends on both the energy spectrum of electrons and ions in the space environment and the electrical properties of the surface materials (including the energy dependent secondary electron yields). Typical benign equilibrium potentials range &om a few tens of volts positive in interplanetary space to a few volts negative in low Earth orbit. However, spacecraft are known to charge to negative potentials exceeding one to ten kilovolts in some environments and anomalies or system failures due to electrostatic discharges originating from highly charged surfaces becomes a serious concern. This presentation will provide a review of the spacecraft charging process with special emphasis on the role of secondary electrons in controlling the current balance process. Charging examples will include spacecraft in Earth orbit and interplanetary space as well as dust charging on the lunar surface, a phenomenon of importance to future lunar surface operations.

Minow, Joseph I.↗
NASA NTRS1989

Comparison of in situ and Landsat derived reflectance of Alaskan glaciers

Reflectances calculated from TM data and corrected for atmospheric effects correspond with in situ measured reflectances in the nadir-viewing mode, and are shown to be related to a glacier's mass balance if measured over a period of years. A reflectance of 0.895 for a test site in the Wrangell Mountains, Alaska, was calculated from TM Band 4 (0.76 - 0.90 micron) data and corrected for atmospheric effects. This value was comparable to the in situ reflectance of 0.90 measured in the same 0.76 - 0.90 micron wavelength region. For the same site, a reflectance value of 0.79 derived from integrating over most (0.40 - 3.0 micron) of the reflective portion of the electromagnetic spectrum was quite different from the integrated reflectance of 0.95 calculated for the spectral range 0.40 - 1.0 micron. This demonstrates the importance of using the full reflective energy spectrum for calculating the albedo of snow, and for obtaining a meaningful computation of a glacier's energy and mass balance change.

Hall, D. K.↗
DOE OSTI2023

Spectral gratings-based phase-contrast imaging for materials characterization

Spectral X-ray detectors provide a direct observation of the energy spectrum of a transmitted X-ray beam, both for typical and phase-contrast gratings-based systems. The sensitivity of a gratings-based X-ray system to small-angle deflections from a given particle size is dependent on X-ray energy. Therefore, spectral (energy-sensitive) detectors could be sensitive to particle size, even with a broad spectrum from a commercial X-ray generator. Furthermore, these detectors allow direct observation of how the X-ray spectrum is changing as the beam is passing through an object and gratings, and how this affects grating visibilities used to determine the presence of small-angle deflections. This is a particular issue for higher-energy systems where artifacts from beam hardening are common. We present results exploring the particle-size dependent signatures that are available from a spectral gratings-based phase-contrast X-ray imaging system, and the feasibility of observing them with lab-based, broad-spectrum X-ray generators.

Gilbert, Andrew J.↗
NASA NTRS1973

Particle entry into the equatorial magnetosphere.

Explorer-45 data are reviewed which concern the behavior and dynamics of protons associated with the storm-time and quiet-time extraterrestrial ring current at the equatorial plane. The quiet-time proton energy spectrum exhibits a peak in the interval between 100 and 200 keV. During storm conditions, the intensities of the higher energy protons decrease while the intensities of protons from 10 to 100 keV are greatly enhanced, making them the dominant contributor to the storm-time particle energy density. It is shown that during magnetic storms, the ratio of the particle energy density to the magnetic field energy density reaches values greater than unity, and that the plasmasphere has a strong influence on the characteristics of particle injection.

Fritz, T. A.↗
NASA NTRS1985

Energetic ions upstream of Jupiter's bow shock

In an analysis of the Jovian ion events, Baker et al. (1984) have found that there appears to be a spectral hardening as the interplanetary magnetic field (IMF) changed orientation from the postnoon to a prenoon connection point. It was also observed that ion events were accompanied by long-period (approximately 10 min) waves whose presence was weakly related to a decrease in the ion anisotropy. The present investigation examines in substantial detail the development of the ion energy spectrum over the full range (approximately 30 keV to approximately 4 MeV). The results of the investigation show that the energy spectra are dominated by heavy ions (presumed to be oxygen and sulfur) at higher (approximately equal to or greater than 300 keV) energies.

Krimigis, S. M.↗
NASA NTRS2000

Estimating Cosmic Ray Spectral Parameters from Simulated Detector Responses

A simple power law model consisting of a single spectral index al is believed to be an adequate description of the galactic cosmic ray (GCR) proton flux at energies below 100 TeV, with a transition at kink energy Ek to a steeper spectral index a2>al above Ek. The maximum likelihood procedure is developed for estimating these three spectral parameters of the broken power law energy spectrum from simulated detector responses. These estimates and their surrounding statistical uncertainty are being used to derive the requirements in energy resolution, calorimeter size, and energy response of a proposed sampling calorimeter for the Advanced Cosmic-ray Composition Experiment for the Space Station (ACCESS). This study thereby permits instrument developers to make important trade studies in design parameters as a function of the science objectives, which is particularly important for space-based detectors where physical parameters, such as dimension and weight, impose rigorous practical limits to the design envelope.

Howell, Leonard↗
NASA NTRS2000

Estimating Cosmic Ray Spectral Parameters From Simulated Detector Responses With Detector Design Implications

A simple power law model consisting of a single spectral index alpha (sub 1), is believed to be an adequate description of the galactic cosmic ray (GCR) proton flux at energies below 10(exp 13) eV, with a transition at knee energy E(sub k) to a steeper spectral index alpha(sub 2) greater than alpha(sub 1) above E(sub k). The maximum likelihood procedure is developed for estimating these three spectral parameters of the broken power law energy spectrum from simulated detector responses. These estimates and their surrounding statistical uncertainty are being used to derive the requirements in energy resolution, calorimeter size, and energy response of a proposed sampling calorimeter for the Advanced Cosmic ray Composition Experiment for the Space Station (ACCESS). This study thereby permits instrument developers to make important trade studies in design parameters as a function of the science objectives, which is particularly important for space-based detectors where physical parameters, such as dimension and weight, impose rigorous practical limits to the design envelope.

Howell, L. W.↗
NASA NTRS2001

Estimating Cosmic-Ray Spectral Parameters from Simulated Detector Responses with Detector Design Implications

A simple power law model consisting of a single spectral index (alpha-1) is believed to be an adequate description of the galactic cosmic-ray (GCR) proton flux at energies below 10(exp 13) eV, with a transition at knee energy (E(sub k)) to a steeper spectral index alpha-2 > alpha-1 above E(sub k). The maximum likelihood procedure is developed for estimating these three spectral parameters of the broken power law energy spectrum from simulated detector responses. These estimates and their surrounding statistical uncertainty are being used to derive the requirements in energy resolution, calorimeter size, and energy response of a proposed sampling calorimeter for the Advanced Cosmic-ray Composition Experiment for the Space Station (ACCESS). This study thereby permits instrument developers to make important trade studies in design parameters as a function of the science objectives, which is particularly important for space-based detectors where physical parameters, such as dimension and weight, impose rigorous practical limits to the design envelope.

Howell, L. W.↗
DOE OSTI2020

Neutron Spectrum Determination for the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) with a Multi-Sphere Spectrometer

This report presents the work that was performed to determine the neutron energy spectrum (spectrum) of the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) with a neutron Multi-Sphere Spectrometer (MSS). The spectrometer measurements were performed when the generator is in an INL Materials and Fuels Complex (MFC) laboratory. The measurements were used in a spectrum unfolding software to calculate the neutron spectrum. Based on initial testing of the MSS spectrometer and experience with the unfolding software, an MMRTG spectrum is reported and a justification for the spectrum is provided.

46 - INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AN↗
NASA NTRS1977

Intensity of primary cosmic-ray electrons of energy exceeding 8 GeV

Results are reported for measurement of the intensity and energy spectrum of primary cosmic-ray electrons with a spark-chamber-counter-emulsion detector flown at a mean altitude of 3 g/sq cm residual atmosphere. A least-squares fit to the flight data yields an electron spectrum from 8 to 80 GeV of approximately 93E to the -2.91 power electrons/sq m/sec per sr/GeV. The results are compared with those of previous experiments as well as with the spectrum obtained for galactic nonthermal radiation. It is concluded that a 'clumpy' magnetic field proportional to the square root of matter density is consistent with measurements of high-energy electrons and synchrotron radiation toward the center of the Galaxy, that a gradual steepening of the electron spectrum relative to the proton spectrum is consistent with an electron lifetime of 1 million years, and that the density of cosmic-ray nucleons and electrons should be essentially uniform throughout the Galaxy if the nucleons have the same lifetime as the electrons and if they traversed 4 to 5 g/sq cm in that lifetime.

Freier, P.↗
DOE OSTI2020

Improved Cumulative Fission Yield Measurements with Fission Spectrum Neutrons on 238U

Two isotopically-characterized targets of high-purity (99.961±0.002%) 238U metal and a neutron dosimetry package were exposed to a pulsed neutron irradiation using the Godiva IV critical assembly at the National Criticality Experiments Research Center to measure the integral fission product yields produced in a Watt fission neutron-energy spectrum. Following irradiation, the fissioned targets were counted with two broad energy germanium detectors. Estimates of the total fissions for each target were made using measurements of well-known fission products. The total number of fissions in each target were then used to measure the fission yields of 33 fission products, 18 of which are published as new measurements. Twelve of the 18 isotopes were in agreement with ENDF/B- VIII.0 using the zeta test and treating ENDF/B-VIII.0 as the true mean: 84mBr, 93Y, 94Y, 104Tc, 134I, 135I, 138Xe, 141Ba, 142Ba, 142La, 146Ce, and 149Nd. The ENDF/B-VIII.0 fission yield for 139Ba was only slightly outside of 1-s relative to the uncertainty measured in this work. Uncertainties for 5 fission product yields were markedly improved over those reported in ENDF/B-VIII.0: 128Sn, 129Sb, 130gSb, 131mTe, and 133I. The fission yields measured for 128Sn, 131mTe, and 133I were in good agreement with the ENDF/B-VIII.0 predicted fission yields. However, fission yields measurements of the isotopes 129Sb, and 130gSb deviated from the ENDF/B-VIII.0 value. Both of these isotopes reside near the doubly magic nuclear shell closures of 50 protons and 82 neutrons. These fission yields may be suppressed because of the odd-odd nuclear structure of 130gSb and the odd-even structure of 129Sb and isomer splitting. Comparisons to other recent work and a brief review with citations are included to support this conclusion.

Fission Yields↗
NASA NTRS2003

High Energy Emission From Millisecond Pulsars

Emission at X-ray and gamma-ray energies has been detected from millisecond pulsars, both isolated and in binary systems. Although these pulsars have low surface magnetic fields, their short periods allow them to have large magnetospheric potential drops, so that high-energy emission from these sources is not unexpected. In fact, several nearby energetic millisecond pulsars that have been detected in X-rays could easily have been detected in gamma-rays by EGRET, but they were not. The reason for this may lie in a high-energy spectrum that is very different in these sources from that of normal pulsars. Both polar cap and outer gap models predict a two-component spectrum, one component peaking in hard X-rays and the other peaking above 1 GeV, with a gap at EGRET peak sensitivity. I will discuss the models for high-energy emission from millisecond pulsars, highlighting the differences between polar cap and outer gap models in spectrum and geometry of the emission.

Harding, Alice K.↗
DOE OSTI2024

Guided Mode Evolution and Ionization Injection in Meter-Scale Multi-GeV Laser Wakefield Accelerators

Here, we show that multi-GeV laser wakefield electron accelerators in meter-scale, low density hydrodynamic plasma waveguides operate in a new nonlinear propagation regime dominated by sustained beating of lowest order modes of the ponderomotively modified channel; this occurs whether or not the injected pulse is linearly matched to the guide. For a continuously doped gas jet, this emergent mode beating effect leads to axially modulated enhancement of ionization injection and a multi-GeV energy spectrum of multiple quasimonoenergetic peaks; the same process in a locally doped jet produces single multi-GeV peaks with <10% energy spread. A three-stage model of drive laser pulse evolution and ionization injection characterizes the beating effect and explains our experimental results.

43 PARTICLE ACCELERATORS↗
NASA NTRS1985

Low-energy gamma rays from Cygnus X-1

The Cyg X-1 was observed by the balloonborne telescope OPALE, in June 1976. The high energy spectrum of the source, which was in its superlow state, was seen to extend well beyond 1 MeV. The observed low energy gamma ray component of Cyg X-1 is compared with the predictions of recent models involving accretion onto a stellar black hole, and including a possible contribution from the pair annihilation 511 keV gamma ray line.

Roques, J. P.↗
DOE OSTI2024

Spectrum and extension of the inverse-Compton emission of the Crab Nebula from a combined Fermi -LAT and H.E.S.S. analysis

The Crab Nebula is a unique laboratory for studying the acceleration of electrons and positrons through their non-thermal radiation. Observations of very-high-energy γ rays from the Crab Nebula have provided important constraints for modelling its broadband emission. We present the first fully self-consistent analysis of the Crab Nebula’s γ-ray emission between 1 GeV and ∼100 TeV, that is, over five orders of magnitude in energy. Using the open-source software package GAMMAPY, we combined 11.4 yr of data from the Fermi Large Area Telescope and 80 h of High Energy Stereoscopic System (H.E.S.S.) data at the event level and provide a measurement of the spatial extension of the nebula and its energy spectrum. We find evidence for a shrinking of the nebula with increasing γ-ray energy. Furthermore, we fitted several phenomenological models to the measured data, finding that none of them can fully describe the spatial extension and the spectral energy distribution at the same time. Especially the extension measured at TeV energies appears too large when compared to the X-ray emission. Our measurements probe the structure of the magnetic field between the pulsar wind termination shock and the dust torus, and we conclude that the magnetic field strength decreases with increasing distance from the pulsar. We complement our study with a careful assessment of systematic uncertainties.

79 ASTRONOMY AND ASTROPHYSICS↗