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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Magnetic Microcalorimeter Gamma-Detectors for High-Accuracy Nuclear Decay Data

Magnetic microcalorimeters (MMCs) are low-energy gamma-ray detectors with ultra-high energy resolution that are operated at temperatures below 50 mK. They use metallic Au absorbers and paramagnetic Ag:Er sensors to measure gamma-ray energies from an increase in detector temperature. Ultra-low temperatures are made accessible to non-expert users with “dry” dilution refrigerators that replace the traditional liquid N 2 and He pre-cooling with a mechanically cooled pulse-tube refrigerator. Our MMC gamma detectors have achieved an energy resolution below 40 eV FWHM at 60 keV, and they have a uniform and reproducible response function that allows adding spectra from different detector pixels without loss in energy resolution. These properties make MMCs well-suited to re-measure nuclear decay data with increased precision and smaller systematic errors to increase the accuracy of non-destructive assays (NDA). We present recent MMC gamma-ray spectra of Th-234 to show how MMCs can resolve lines that are relevant for NDA analysis and that overlap in Ge spectra. We also discuss the accuracy that MMCs can achieve for nuclear decay data with an emphasis on gamma-ray energies and intensity ratios that current NDA codes are based on.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1994

Interaction of ultraviolet and X-ray radiation with gamma rays produced by a jet in active galactic nuclei

Recent observations by the Compton Gamma-Ray Observatory give evidence for the existence of a type of blazar with strong gamma-ray emission. Data obtained by EGRET for the quasar 3C 279 show a spectrum between 100 MeV and 10 GeV. Photons of such energies should interact with the X-rays and produce positron/electron pairs. If the optical depth against pair production for the gamma rays is large (tau(gamma gamma) greater than 1), the gamma-ray spectrum should be affected. The importance of this process has been pointed out by, e.g., Maraschi, Ghisellini, & Celotti (1992). Several works (e.g., Dermer 1993; Zbyszewska 1993; Sikora, Begelman, & Rees 1993) concerning gamma-ray radiation from quasar 3C 279 have proposed a model in which the gamma rays are produced via interaction between a moving cloud of relativistic electrons and external soft photons. The presence of gamma rays in active galactic nuclei spectra gives constraints on the localization and the luminosity of the medium which produces ultraviolet/X-ray photons. We investigate what conditions should be fulfilled in the above model to avoid the absorption of the gamma rays due to pair production.

Zbyszewska, Magda↗
DOE OSTI2015

Galactic center γ-ray excess in hidden sector DM models with dark gauge symmetries: local Z{sub 3} symmetry as an example

We show that hidden sector dark matter (DM) models with local dark gauge symmetries make a natural playground for the possible γ-ray excess from the galactic center (GC). We first discuss in detail the GC γ-ray excess in a scalar dark matter (DM) model with local Z{sub 3} symmetry which was recently proposed by the present authors. Within this model, scalar DM with mass 30–70 GeV is allowed due to the newly-opened (semi-)annihilation channels of a DM pair into dark Higgs ϕ and/or dark photon Z′ pair, and the γ-ray spectrum from the GC can be fit within this model. Then we argue that the GC gamma ray excess can be easily accommodated within hidden sector dark matter models where DM is stabilized by local gauge symmetries, due to the presence of dark Higgs (and also dark photon for Abelian dark gauge symmetry)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

GADRAS Detector Response Function.

The Gamma Detector Response and Analysis Software (GADRAS) applies a Detector Response Function (DRF) to compute the output of gamma-ray and neutron detectors when they are exposed to radiation sources. The DRF is fundamental to the ability to perform forward calculations (i.e., computation of the response of a detector to a known source), as well as the ability to analyze spectra to deduce the types and quantities of radioactive material to which the detectors are exposed. This document describes how gamma-ray spectra are computed and the significance of response function parameters that define characteristics of particular detectors.

Mitchell, Dean J.↗
NASA NTRS1974

International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volumes 1 & 2

Topics discussed include diffuse gamma rays, gamma ray sources (in particular, the Crab Nebula and Crab Pulsar), X-ray sources, isotopic and nuclear composition, spectra of nuclei, searches for antinuclei, studies of VH and VVH nuclei, measurements of electrons and positrons, the spectra of high-energy electrons, cosmic gamma rays, cosmic ray sources, interplanetary radial gradients, the theory and observation of electron modulation, short-period cosmic ray intensity variations, atmospheric and coupling effects on neutron monitors and muon telescopes, secondary particles and photons in the atmosphere, harmonics of diurnal variations, geomagnetic effects and cutoffs, planetary and interplanetary effects, solar particle access observations, long-term cosmic ray intensity modulation by solar activity and interplanetary effects, Forbush decreases, modulation and anisotropy of low-energy particles, the theory and models of solar particle propagation, solar flare particle composition, and relativistic solar particles. Individual items are announced in this issue.

Source record↗
NASA NTRS1995

GHRS observations of cool, low-gravity star. 2: Flow and turbulent velocities in the outer atmosphere of gamma CRU CIS (M3.4 III)

The Goddard High Resoulution Spectrograph (GHRS) on the Hubble Space Telescope (HST) has been used to obtain medium (R = 20,000) and high (R = 85,000) resoultion UV spectra of chromosphere emission features for the M3.4 III star gamma Cru. Small Science Aperture (SSA) G270M and Echelle-B spectra of selected regions in the 2300-2850 A range were obtained to determine the kinematics of the chromosphere using lines of C2), Fe2, Co2, Si1/2), Ni2, Mn2, and Mg2. Profiles of C2) (UV 0.01) lines and fluorescently excited lines of low optical depth indicate average turbulent velocities (Doppler FWHM) of 30.2 +/- 1.3 and 28.8 +/- 1.3 km/s, respectively. The fluorescent emission lines (mean RV = 21.3 +/- 0.9 km/s) and the wings of the emission components of Fe2 lines (mean RV = 22.8 +/- 0.4 km/s) are approximately at rest relative to the radial velocity of the star (21 km/s), while the C2) lines show a modest inflow (mean RV = 23.1 +/- 0.9 km/s). The more opaque lines of Fe2 and Mg2 exhibit complex profiles resulting from line formation in an optically thick, extended expanding atmosphere. The emission wings of these lines are broadened by multiple scattering, and they are centered near the photospheric radial velocity. Closer to line center, these strong lines show a strong blueshifted self-absorption feature (already seen in IUE data), indicative of formation in an expanding chromosphere, and a previously unseen dip in the profiles on the red side of line center. The absorption components, when extracted using simple Gaussian fits, show strong correlations with the relative optical depths of the lines. The derived absorption flow velocities converge to the photospheric velocity as one examines spectra features formed deeper in the atmosphere. The blueward abosrption velocity increases in magnitude from about 7 to 14 km/s with increasing line optical depth - the strong absorptions directly map the acceleration of the outflowing stellar wind, while the interpretation of the weaker redshifted abosrptions is more ambiguous, indicating either an inflow of material or formation in an extended, spherically expanding outflow. The Mg2 and Fe2 profiles, taken together, imply that the wind speed decreases between the atmospheric layers where the Mg2 and Fe2 self-absorption components are formed. Interstellar absorptions are seen in the resonance lines of Mg2 (UV 1) and Fe2 (UV1) with zero-volt lower levels, at about -3 km/s, consistent with models of the interstellar medium in the direction of gamma Cru. Finally, we have detected the Mg2 'satellite lines' seen in solar spectra obtained above the limb. In gamma Cru these lines are probably fluorescently excited by H Ly beta.

Carpenter, Kenneth G.↗
DOE OSTI2017

High-redshift Blazars through NuSTAR Eyes

The most powerful sources among the blazar family are MeV blazars. Often detected at z > 2, they usually display high X- and γ -ray luminosities, larger-than-average jet powers, and black hole masses ≳10{sup 9} M {sub ☉}. In the present work, we perform a multiwavelength study of three high-redshift blazars: 3FGL J0325.5+2223 ( z = 2.06), 3FGL J0449.0+1121 ( z = 2.15), and 3FGL J0453.2−2808 ( z = 2.56), analyzing quasi-simultaneous data from GROND, Swift -UVOT and XRT, Nuclear Spectroscopic Telescope Array ( NuSTAR ), and Fermi -LAT. Our main focus is on the hard X-ray band recently unveiled by NuSTAR (3–79 keV) where these objects show a hard spectrum that enables us to constrain the inverse Compton (IC) peak and the jet power. We found that all three targets resemble the most powerful blazars, with the synchrotron peak located in the submillimeter range and the IC peak in the MeV range, and therefore belong to the MeV blazar class. Using a simple one-zone leptonic emission model to reproduce the spectral energy distributions, we conclude that a simple combination of synchrotron and accretion disk emission reproduces the infrared–optical spectra, while the X-ray to γ -ray part is well reproduced by the IC scattering of low-energy photons supplied by the broad-line region. The black hole masses for each of the three sources are calculated to be ≳4 × 10{sup 8} M {sub ☉}. The three studied sources have jet power at the level of, or beyond, the accretion luminosity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE BATSE 5B GAMMA-RAY BURST SPECTRAL CATALOG

We present systematic spectral analyses of gamma-ray bursts (GRBs) detected with the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma-Ray Observatory during its entire nine years of operation. This catalog contains two types of spectra extracted from 2145 GRBs, and fitted with five different spectral models resulting in a compendium of over 19,000 spectra. The models were selected based on their empirical importance to the spectral shape of many GRBs, and the analysis performed was devised to be as thorough and objective as possible. We describe in detail our procedures and criteria for the analyses, and present the bulk results in the form of parameter distributions. This catalog should be considered an official product from the BATSE Science Team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC)

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

Recent comet impacts on the moon - The evidence from remote-sensing studies

Multispectral images and near-infrared reflectance spectra were obtained for the Reiner Gamma Formation, a swirllike albedo and magnetic anomaly in the western portion of the lunar near side, as well as for nearby geologic units in Oceanus Procellarum, using the University of Hawaii 2.24-m telescope at the Mauna Kea Observatory. The spectra of the high albedo swirl material are closely matched by models incorporating 90-95 percent fresh mare basalt with 5-10 percent highlands debris.

Bell, Jeffrey F.↗
DOE OSTI2024

Dual particle imaging: Applications in security and environmental imaging

Radiation imaging detectors have been applied in a variety of fields for detection, localization and characterization of radioactive sources. In this work, we describe a handheld detection system (H2DPI) that can simultaneously image neutrons and gamma rays, and reconstruct the energy spectra of the incident particles. This system was applied to the detection and characterization of a plutonium metal source in experiments performed at the National Criticality Experiments Research Center, where the 4.5 kg plutonium source was placed approximately 60 cm from the H2DPI. Neutron and gamma-ray images were measured that show good agreement with the known location of the source. Furthermore, the H2DPI was also used to measure the neutron spectrum, which shows the expected shape of a Watt fission spectrum, and the gamma-ray energy spectrum, which shows the energies common to plutonium metal. Finally, we describe the application of the H2DPI in augmented reality, whereby real-time neutron and gamma-ray imaging data can be streamed to the Microsoft HoloLens to allow the user to visualize the source locations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Neutron Spectrum Measurements from Irradiations at NCERC

Several irradiations have been conducted on assemblies (COMET/ZEUS and Flattop) at the National Criticality Experiments Research Center (NCERC) located at the Nevada National Security Site (NNSS). Configurations of the assemblies and irradiated materials changed between experiments. Different metallic foils were analyzed using the radioactivation method by gamma-ray spectrometry to understand/characterize the neutron spectra. Results of MCNP calculations are shown. It was concluded that MCNP simulated spectra agree with experimental measurements, with the caveats that some data are limited by statistics at low-energies and some activation foils have low activities.

42 ENGINEERING↗
DOE OSTI2016

SYNCHROTRON ORIGIN OF THE TYPICAL GRB BAND FUNCTION—A CASE STUDY OF GRB 130606B

We perform a time-resolved spectral analysis of GRB 130606B within the framework of a fast-cooling synchrotron radiation model with magnetic field strength in the emission region decaying with time, as proposed by Uhm and Zhang. The data from all time intervals can be successfully fit by the model. The same data can be equally well fit by the empirical Band function with typical parameter values. Our results, which involve only minimal physical assumptions, offer one natural solution to the origin of the observed GRB spectra and imply that, at least some, if not all, Band-like GRB spectra with typical Band parameter values can indeed be explained by synchrotron radiation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

Constraints on gamma-ray bursters from soft X-ray transients

The Columbia Astrophysics Laboratory's Einstein imaging proportional counter database has been searched for possible X-ray counterparts to gamma ray bursts. The limiting sensitivity was about 10 to the 10th erg/sq cm with a total exposure of about 3 x 10 to the 6th s divided among about 1000 1 deg x 1 deg fields. Four events with a pointlike spatial distribution were detected but their extremely soft spectra makes them unlikely candidates for gamma ray burst counterparts. The results are used to place limits on the X-ray and gamma ray luminosity ratio and log(number)N-log(flux)S relation for gamma ray bursts. The constraints placed on models for their origin are commented on.

Helfand, D. J.↗
DOE OSTI2022

Monte Carlo simulations demonstrating physics of equivalency of gamma, electron-beam, and X-ray for radiation sterilization

We report the sterilization of medical devices using the gamma rays from the decay of cobalt-60 has accumulated decades of experience of the performance of the materials and devices that are irradiated. The use of radiation using electron beams and x-rays has much less experience and this leads to questions of equivalency between these three technologies. Computer simulations were conducted to model the relevant physical processes of the interactions of each of the three forms of radiation in order to compare the spectra of electron energies at energies below 500 keV. It is predominantly the electrons below this threshold that produce the sterilization dose. No difference in energy spectra was seen between the three types of initial radiation. It is concluded that there is no energy dependent difference between gamma, e-beam, and x-ray for radiation sterilization.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

SU-E-T-186: Feasibility Study of Glass Cherenkov Detector for Prompt Gamma Detection in Proton Therapy

Purpose: To simulate a Cherenkov glass detector system utilizing prompt gamma (PG) technique to quantify range uncertainties in proton radiation therapy. Methods: A simulation of high energy photons typically produced in proton interactions with materials incident onto a block of Cherenkov glass was performed with the Geant4 toolkit. The standard electromagnetic package was used along with several decay modules (G4Decay, G4DecayPhysics, and G4RadioactiveDecayPhysics) and the optical photon components (G4OpticalPhysics). Our setup included a pencil beam consisting of a hundred thousand 6 MeV photons (approximately the deexcitation energy released from 16O) incident onto a 2.5 ⊗ 2.5 ⊗ 1.5 cm3 of a Cherenkov glass (7.2 g of In2O3 + 90 g cladding, density of 2.82 g/cm3, Zeff = 33.7, index of refraction 1.56). The energy deposited from incident 6 MeV photons as well as secondary electrons and resulting optical photons were recorded. Results: The energy deposited by 6 MeV photons in glass material showed several peaks that included the photoelectric, the single and double escape peaks. About 11% of incident photons interacted with glass material to deposit energy. Most of the photons collected were in the region of double escape peak (approximately 4.98 MeV). The secondary electron spectrum produced from incident photons showed a high energy peak located near 6 MeV and a sharp peak located ∼120 keV with a continuous distribution between these two points. The resulting Cherenkov photons produced showed a continuous energy distribution between 2 and 5 eV with a slight increase in yield beginning about 3 eV. The amount of Cherenkov photons produced per interacting incident 6 MeV photon was ∼240.7. Conclusion: This study suggests the viability of utilizing the Cherenkov glass material as a possible prompt gamma photon detection device. Future work will include optimization of the detector system to maximize photon detection efficiency.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Advanced nanoscale characterization of aluminum nanoparticles with modified surface morphology via atmospheric helium and carbon monoxide plasmas

Aluminum nanoparticles (nAl) have the potential as energetic additives in explosive/propellant formulations. Scalable methodologies must be pursued to mitigate the inactive amorphous alumina shell surrounding the active aluminum (Al) core with modified surface morphology and chemistry for increased combustion effects. This work explores the feasibility of making reactive core/shell nAl with thinned oxide shells and modified surface coatings via a two-step atmospheric plasma surface treatment process in a custom dielectric barrier discharge plasma reactor. The commercial nAl of nominal average size similar to 40-60nm was first treated with helium (He) followed by He/carbon monoxide (CO) plasmas for different durations. The resultant samples were characterized via high-resolution transmission electron microscopy (HRTEM) and Fourier transform IR (FTIR) spectra. HRTEM images revealed sporadic patchy gamma -alumina deposits on particle surfaces and in gaps among particles for all samples, suggesting the non-uniform plasma effects of the He/CO glow. Nanoscale chemical analyses via scanning transmission electron microscopy elemental mapping and x-ray energy dispersive spectroscopy were further performed. Although no carbon-associated structure appeared in electron energy loss spectroscopy (EELS) spectra, the presence of carbonaceous materials was confirmed as a thin dispersive layer evenly distributed on the nAl surface suggesting either its amorphous nature or is present at a level insufficient to generate satisfactory EELS spectra. The trend of intensity profiles for key elements acquired by drawing lines across a single particle on the elemental maps confirmed that carbonaceous materials only existed on the surface and they were most likely carboxylates that increased with increased He/CO treatment duration, as evident by FTIR results. Finally, this work demonstrated the success of atmospheric plasma-treated reactive nAl with comprehensively characterized surface features via advanced microscopy and spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Gamma ray irradiated AgFeO{sub 2} nanoparticles with enhanced gas sensor properties

AgFeO{sub 2} nanoparticles were synthesized via a facile hydrothermal method and irradiated by various doses of gamma ray. The products were characterized with X-ray powder diffraction, UV–vis absorption spectrum and transmission electron microscope. The results revealed that the crystal structure, morphology and size of the samples remained unchanged after irradiation, while the intensity of UV–Vis spectra increased with irradiation dose increasing. In addition, gamma ray irradiation improved the performance of gas sensor based on the AgFeO{sub 2} nanoparticles including the optimum operating temperature and sensitivity, which might be ascribed to the generation of defects. - Graphical abstract: Gamma ray irradiation improved the performance of gas sensor based on the AgFeO{sub 2} nanoparticles including sensitivity and optimum operating temperature, which might be ascribed to the generation of defects. - Highlights: • AgFeO{sub 2} nanoparticles were synthesized and irradiated with gamma ray. • AgFeO{sub 2} nanoparticles were employed to fabricate gas sensors to detect ethanol. • Gamma ray irradiation improved the sensitivity and optimum operating temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

AN EMPIRICAL DETERMINATION OF THE INTERGALACTIC BACKGROUND LIGHT FROM UV TO FIR WAVELENGTHS USING FIR DEEP GALAXY SURVEYS AND THE GAMMA-RAY OPACITY OF THE UNIVERSE

We have previously calculated the intergalactic background light (IBL) as a function of redshift from the Lyman limit in the far-ultraviolet to a wavelength of 5 μ m in the near-infrared range, based purely on data from deep galaxy surveys. Here, we use similar methods to determine the mid- and far-infrared IBL from 5 to 850 μ m. Our approach enables us to constrain the range of photon densities by determining the uncertainties in observationally determined luminosity densities and spectral gradients. By also including the effect of the 2.7 K cosmic background photons, we determine upper and lower limits on the opacity of the universe to γ -rays up to PeV energies within a 68% confidence band. Our direct results on the IBL are consistent with those from complimentary γ -ray analyses using observations from the Fermi γ -ray space telescope and the H.E.S.S. air Čerenkov telescope. Thus, we find no evidence of previously suggested processes for the modification of γ -ray spectra other than that of absorption by pair production alone.

79 ASTRONOMY AND ASTROPHYSICS↗