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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Solar flare gamma-ray line profiles

Solar gamma-ray lines are produced through collisions of pairs of positive ions whose center of mass energies are above the relevant thresholds for excitation of gamma-ray emitting states. Because of the low density of the solar plasma, prompt gamma rays are emitted by recoiling ions before significant energy loss has occurred. Thus, the lines are expected to be Doppler-broadened to widths of the order of a hundred KeV. Gamma-ray lines resulting from proton and alpha-particle (He-4 ion) beams on carbon and oxygen targets in the laboratory exhibit complex profiles which change rapidly with the gamma-ray observation angle. Earlier work has been limited to modeling laboratory and solar flare gamma-ray profiles produced by proton excitation, but laboratory profiles of the carbon 4.44-MeV line and oxygen 6.13-MeV line from alpha excitation have now been successfully modeled. Solar flare gamma-ray line profiles of the carbon and oxygen lines from heavy ions in the ambient solar medium interacting with representative high-energy proton and alpha particle populations are presented.

Lang, F. L.↗
NASA NTRS1989

Monte Carlo models and analysis of galactic disk gamma-ray burst distributions

Gamma-ray bursts are transient astronomical phenomena which have no quiescent counterparts in any region of the electromagnetic spectrum. Although temporal and spectral properties indicate that these events are likely energetic, their unknown spatial distribution complicates astrophysical interpretation. Monte Carlo samples of gamma-ray burst sources are created which belong to Galactic disk populations. Spatial analysis techniques are used to compare these samples to the observed distribution. From this, both quantitative and qualitative conclusions are drawn concerning allowed luminosity and spatial distributions of the actual sample. Although the Burst and Transient Source Experiment (BATSE) experiment on Gamma Ray Observatory (GRO) will significantly improve knowledge of the gamma-ray burst source spatial characteristics within only a few months of launch, the analysis techniques described herein will not be superceded. Rather, they may be used with BATSE results to obtain detailed information about both the luminosity and spatial distributions of the sources.

Hakkila, Jon↗
DOE OSTI2026

Interpolation of computed gamma-ray detector response functions

Gamma-ray spectra measured by traditional detectors contain features that result from a combination of the effects of detector materials/geometry, the incident gamma-ray energy, and the angle of entry. The features, such as the full-energy photopeak, Compton continuum, annihilation peak, and escape peaks, are governed by simple relationships depending on incident energy and have been known for a long time. Monte Carlo computer simulations of gamma rays interacting with a detector will show these features, and with a resolution function applied, the results should look similar to real measurements. The traditional approach to creating a detector response function requires many separate simulations of monoenergetic gamma rays striking the detector. This paper presents a new approach to developing computed detector response functions. The new approach involves a much smaller number of monoenergetic gamma-ray simulations and uses interpolation to quickly generate the responses of gamma rays that were not simulated. During the interpolation process, the underlying physics equations are used to accurately compute the response of a given energy gamma ray from the small set of simulations. Such work enables accelerated generation of synthetic radiation detector data.

Detector response↗
DOE OSTI2020

The Effect of Laser Treatment on the Morphology of Graphene/CdTe X-Ray and gamma-Ray Detectors

Peculiarities of morphology and electric properties of X-ray and γ-ray detectors developed by graphene deposition onto commercially available (111) oriented CdTe:Cl wafers has been investigated. Laser treatment of graphene contact using millisecond YAG-laser with an energy density of 0.1-4.5 J/cm2 has been carried out in order to modify and improve their structure and phase state

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Investigation of the \(\gamma \)-ray Properties of the \(2^+\) States in \(^{14}\)C

The properties of the 2$^+_1$ and 2$^+_2$ excited states in 14 C were studied in an experiment conducted at Argonne National Laboratory. A 9 Be( 6 Li,pγ) fusion-evaporation reaction and the GRETINA-ORRUBA setup were employed to populate states of 14 C and detect γ-particle coincidence events. Finally, the precise determination of the 2$^+_1$ level energy, complemented by the estimation of the γ-ray branch of the 2$^+_2$ near-threshold state, will serve as a benchmark to test the Shell Model Embedded in the Continuum calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1976

Large-area multi-crystal NaI/Tl/ detectors for X-ray and gamma-ray astronomy

An array of large multicrystal NaI(Tl) detectors was constructed and used in a balloon-borne experiment to observe weak transient bursts of cosmic origin. The array had an active area of about 1 sq m and was sensitive to photons above 50 keV. Localized bursts which were observed are attributed to long-lived phosphorescence following large energy deposits by cosmic rays in the crystals.

Fishman, G. J.↗
NASA NTRS1978

Low-intensity x-ray and gamma-ray imaging device

Low-dosage, low-power X-ray system can be made completely self-contained, allowing fluoroscopy and radiography to be carried out in field and remote locations. New device, known as "lixiscope," can be used with conventional X-ray machine turned down to low level, or, it can be operated with radioisotope source for hand-held portable applications. Originally developed for X-ray astronomy, lixiscope obtains high sensitivity by using intermediate stages of photoelectron conversion and electron amplification to generate image suitable for direct viewing or for recording on film.

Yin, L. I.↗
NASA NTRS1979

Low intensity X-ray and gamma-ray imaging device

A radiation to visible light converter is combined with a visible light intensifier. The converter is a phosphor or scintillator material which is modified to block ambient light. The intensifier includes fiber optics input and output face plates with a photocathode-microchannel plate amplifier-phosphor combination. Incoming radiation is converted to visible light by the converter which is piped into the intensifier by the input fiber optics face plate. The photocathode converts the visible light to electrons which are amplified by a microchannel plate amplifier. The electrons are converted back to light by a phosphor layer and piped out for viewing by the output fiber optics faces plate. The converter-intensifier combination may be further combined with its own radiation source or used with an independent source.

Yin, L. I.↗
NASA NTRS1981

A new method for focusing and imaging X-rays and gamma-rays with diffraction crystals

Bent diffraction crystals in which the intercrystalline-plane spacing is varied as a function of position in the crystal are used to focus monochromatic radiation from a point source or parallel beam down to a point image. Conversely, radiation from a point source can be focused into an outgoing parallel beam. The Bragg angle for diffraction of monochromatic radiation will now vary as a function of position in the crystal and this new degree of freedom is used to obtain focusing and imaging of the diffracted beam. This approach to focusing and imaging is applied to the design of a large-area, high resolution X-ray telescope that is also a high resolution monochromator with the unique feature that the width of the energy increment that is diffracted can be controlled and varied during the operation of the instrument. The field can be scanned with a wide energy increment and then switched to a narrow energy increment for the high resolution work. Both transmission and reflection type diffraction crystals can be used.

Smither, R. K.↗
NASA NTRS1982

The temperature of thermal X-ray and gamma-ray sources

The temperature of a source can be accurately measured, assuming that it is optically thin and exhibits a bremsstrahlung, on the basis of the shape of its spectral distribution. An explicit relation is derived for the temperature in terms of this slope, and as a sum of correction terms to the limiting form of the bremsstrahlung formula. The corrections can be evaluated easily in terms of simple, accurate asymptotic formulae. For the case where there is a distribution of temperatures in the plasma, an additional correction is derived in terms of the rms variation in the plasma temperature. Corrections due to a modified Bessel function, the Born approximation, plasma electron energy distribution and electron-electron bremsstrahlung are discussed

Gould, R. J.↗
NASA NTRS1982

X-ray and gamma-ray upper limits for pulsed emission from radio pulsars

Results are given for an HEAO 1 search for pulsed emissions from 11 radio pulsars, in the 15 keV-11 MeV energy range. The upper limits of the Vela pulsar are found to fall below the low-energy extrapolation of the more than 50 MeV pulsed spectrum observed by the COS B satellite, and while consistent with predictions of a polar cap acceleration model, seem barely consistent with a single power-law interpolation between optical intensity and the 50 MeV intensity. High energy X-ray upper limits for seven of the ten other pulsars, which were chosen on the basis of proximity to earth, high rotational energy loss rates and short periods, are found to be only a few percent of their rotational energy losses, assuming a moment of inertia, an emission solid angle, and a pulse duty cycle, that are all similar to the high energy X-ray duty cycle of the Crab pulsar. These upper limits are below the corresponding fraction for the Crab pulsar in the cases of the Vela pulsar, PSR 1929+10 and PSR 1642-03.

Knight, F. K.↗
NASA NTRS1985

Power-law X-ray and gamma-ray emission from relativistic thermal plasmas

A common characteristic of cosmic sources is power-law X-ray emission. Extragalactic sources of this type include compact components of active galactic nuclei (AGN). The present study is concerned with a theoretical model of such sources, taking into account the assumption that the power-law spectra are produced by repeated Compton scatterings of soft photons by relativistic thermal electrons. This is one of several possible physical mechanisms leading to the formation of a power-law spectrum. Attention is given to the Comptonization of soft photon sources, the rates of pair processes, the solution of the pair equilibrium equation, and the constraints on a soft photon source and an energy source. It is concluded that the compactness parameters L/R of most of the cosmic sources observed to date lie below the maximum luminosity curves considered.

Zdziarski, A. A.↗
NASA NTRS1987

A long-duration balloon payload for hard X-ray and gamma-ray observations of the sun

A balloon payload designed to study the processes of energy release, particle acceleration, and heating of the active corona in hard X-ray microflares and normal flares is described. An array of liquid nitrogen-cooled germanium detectors together with large area phoswich scintillation detectors provide the highest sensitivity (about 500 sq cm) and energy resolution (not greater than 0.7 keV) ever achieved for solar hard X-ray (about 15-600 keV) measurements. These detectors were flown in February 1987 from Australia on a long duration radiation controlled balloon flight (LDBF) which provided 12 days of observations before cutdown in Brazil. The payload includes solar cells for power, pointing, and navigation sensors, a microprocessor controlled data system with VCR tape storage, and transmitters for GOES and ARGOS spacecraft. This successful flight illustrates the potential of LDBFs for solar flare studies.

Lin, R. P.↗
NASA NTRS1993

Optical, X-ray and gamma-ray observations of compact objects in globular clusters

In the past three years, a new era of study of globular clusters has begun with multiwavelength observations from the current generation of astronomical telescopes in space. We review the recent results obtained from our studies of compact binaries and x-ray sources in globulars with ROSAT and Hubble Space Telescope (HST) as well as our balloon-borne hard x-ray telescope EXITE (Energetic X-ray Imaging Telescope Experiment) and ground-based observations (CTIO). With ROSAT, we have obtained the most sensitive high resolution soft x-ray images of clusters which show multiple low luminosity sources in cluster cores that are likely indicative of the long-sought population of cataclysmic variables (CVs). We have obtained deep H-alpha images of two clusters with HST and found CV candiates for 3 of the ROSAT sources in the core of NGC 6397. New CTIO imaging and spectroscopy of two 'dim source' fields in omega-Cen are also described. With EXITE we carried out the first hard x-ray imaging observations of the cluster 47 Tuc; such studies can ultimately limit the populations of millisecond pulsars and pulsar emission mechanisms. A long ROSAT exposure on 47 Tuc also shows probable cluster diffuse emission, possibly due to hot gas from ablating millisecond pulsars. Multiwavelength studies of globular clusters may provide new constraints on problems as diverse as the origin of CVs and low mass X-ray binaries (LMXBs) and the origin of hot gas in globulars.

Grindlay, J. E.↗