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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

On the determination of the cosmic infrared background radiation from the high-energy spectrum of extragalactic gamma-ray sources

In a recent paper Stecker, De Jager, & Salamon have suggested using the observed approximately MeV to TeV spectra of extragalactic gamma-ray sources as probes of the local density of the cosmic infrared background radiation (CIBR) and have subsequently claimed a first possible measurement of the CIBR from the analysis of the gamma-ray spectrum of Mrk 421 (De Jager, Stecker, & Salamon). The CIBR from normal galaxies consists of two components: a stellar emission component (CIBRs), and a thermal dust emission component (CIBRd). Photons with energies in the approximately 0.1-2 TeV range interact primarily with the CIBRs, whereas interactions with CIBRd dominate the absorption of photons in the approximately 2-100 TeV energy range. SDS 92 and DSS94 considered only the interaction of the gamma-rays with the dust emission component of the CIBR. We present here an improved analysis of the absorption of extragalactic TeV gamma rays by the CIBR, taking the dual nature of its origin into account. Applying the analysis to the observed gamma-ray spectrum of Mrk 421, a BL Lac object at z = 0.031, we find agreement with DSS94 tentative evidence for absorption by the CINRs. Our analysis therefore limits the detection of the CIBR to the approximately 15-40 micron wavelength regime which, considering the uncertainties in the highest energy (greater than 4 TeV) data and ion the possibility of absorption inside the source, many turn out to be an upper limit on its energy density. At shorter wavelengths (lambda approximately = 1-15 microns), where the gamma-ray interactions are dominated by the CIBRs, our analysis definitely yields only an upper limit on the energy density of the CIBR. In contrast, DSS94 have claimed a possible first measurement of the CIBR over the entire 1-120 micron wavelength region. The upper limit on the CIBRs and tentative detection of the CIBRd are consistent with normal galaxies contributing most of the energy to the CIBR, and constrain the contribution of some exotic sources. With careful modeling of infrared foreground emissions, these constraints on the CIBR are above the values measurable by the DIRBE experiment on board the Cosmic Background Explorer (COBE) satellite.

Dwek, Eli↗
NASA NTRS1974

Radio astronomy

The origins, generation, detection, and interpretation of radio signals are discussed for signals with an assumed random polarization. After defining the basic parameters, the discussion moves to such topics as synchrotron radiation, plasma effects, changes in the electron energy spectrum in the radiating regions, energy loss to ionization, bremsstrahlung, radio astronomical observations of high-energy particles, emission by energetic particles, observation of supernova remnants and pulsars, galactic background continuum radiation, and others.

Alexander, J.↗
NASA NTRS2006

Radiation measured with TEPC and CR-39 PNTDs in low Earth orbit

The radiation impact to astronauts depends strongly on the particles linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field in low Earth orbit (LEO) and the influence of radiation on astronauts. The best active dosimeter used for all LET is the tissue equivalent proportional counter (TEPC); the best passive dosimeter used for high LET is CR-39 plastic nuclear track dosimeter (PNTD). TEPC and CR-39 PNTDs were used to investigate the radiation in LEO. LET spectra and radiation quantities were obtained for STS-112 and STS-114 missions with TEPC and CR-39 PNTDs. This paper introduces the operation principles for the two types of dosimeters, presents radiation results measured and compares the results obtained with different dosimeters.

Zhou, D.↗
NASA NTRS1972

Radiative pion capture by C12.

The energy spectrum of neutrons from radiative pion capture by carbon is investigated. Radiative pion capture is identified by coincidence of a stop signal and a signal from one of six lead-glass gamma detectors when negative pions traverse a beam telescope and are stopped in a carbon target. The energy of the neutrons is measured using the time interval between a stop signal coincident with a gamma-counter signal and a signal from a liquid-oscillator neutron counter. Asymmetry in the neutron-photon angular correlation increases with neutron energy and is accounted for by direct neutron emission.

Lam, W. C.↗
NASA NTRS1983

The solar O III spectrum. II - Longer wavelengths, line widths, and the He II Lyman alpha radiation field

The solar O III spectrum above 900 A is analyzed, including several visible and infrared lines which are important in nebular studies. The dependence of the line intensities on the rate of photoexcitation by He Ly-alpha is determined, and the observability of these lines in the solar spectrum is studied. The impact approximation is employed to calculate the expected line widths of the stronger solar O III lines. The photoexciting field at 304 A calculated from the observed intensities of the O III lines below 900 A (Bhatia et al., 1982) is compared with the field predicted by a recent model (Avrett et al., 1976). It is shown that additional radiation trapping must be present beyond that given by this model.

Kastner, S. O.↗
NASA NTRS1992

Spectral-luminosity evolution of active galactic nuclei and the cosmic X- and gamma ray background

Coherent electromagnetic dynamo acceleration processes, which act on charge particles within the context of black hole accretion disk scenarios, are generally regarded as the underlying central power source for active galactic nuclei (AGN). If the precursor active galaxies (PAG) for such AGN are formed at high redshift and contain initial seed black holes with mass approximately equal to 10(exp 4) solar masses, then the Eddington limited X-ray radiation emitted during their lifetime will undergo the phenomenon of 'spectral-luminosity evolution'. When accretion disks are first formed at the onset of galaxy formation the accretion rate occurs at very high values of luminosity/size compactness parameter L/R greater than 10(exp 30) erg/cm-sec. In the absence of extended structure, such high values of L/R generate dynamic constraints which suppress coherent, black hole/accretion disk dynamo particle acceleration processes. This inhibits nonthermal radiation processes and causes the spectrum of X-radiation emitted by PAG to be predominantly thermal. A superposition of PAG sources at z is greater than or equal to 6 can account for the residual cosmic X-ray background (CXB) obtained from the total CXB after subtraction of foreground AGN sources associated with present epoch Seyfert galaxies. The manner in which the PAG undergo spectral-luminosity evolution into Seyfert galaxies is investigated.

Leiter, Darryl↗
NASA NTRS1976

An elementary theory of eclipsing depths of the light curve and its application to Beta Lyrae

An elementary theory of the ratio of depths of secondary and primary eclipses of a light curve has been proposed for studying the nature of component stars. It has been applied to light curves of Beta Lyrae in the visual, blue, and far-ultraviolet regions with the purpose of investigating the energy sources for the luminosity of the disk surrounding the secondary component and determining the dominant radiative process in the disk. No trace of the spectrum of primary radiation has been found in the disk. Therefore, it is suggested that LTE is the main radiative process in the disk, which radiates at a temperature of approximately 12,000 K in the portion that undergoes eclipse. A small source corresponding to 14,500 K has also been tentatively detected and may represent a hot spot caused by hydrodynamic flow of matter from the primary component to the disk.

Huang, S.-S.↗
NASA NTRS1989

Extragalactic radiation and the ultra-high-energy cosmic-ray spectrum

The effect of extragalactic microwave and submillimeter-radiation fields on the ultrahigh-energy cosmic-ray spectrum is reexamined. It is found that the general characteristics of the spectrum can be derived from fairly simple analytical arguments. It is shown that the various spectral features obtained by numerical calculations can be explored by simpler and more general means. This approach is illustrated using a newly derived lifetime-energy relation based on the new submillimeter observations.

Stecker, F. W.↗
NASA NTRS1978

Measurements of the spectrum and energy dependence of X-ray transition radiation

The results of experiments designed to test the theory of X-ray transition radiation and to verify the predicted dependence of the characteristic features of the radiation on the radiator dimensions are presented. The X-ray frequency spectrum produced by 5- to 9-GeV electrons over the range 4 to 30 keV was measured with a calibrated single-crystal Bragg spectrometer, and at frequencies up to 100 keV with an NaI scintillator. The interference pattern in the spectrum and the hardening of the radiation with increasing foil thickness are clearly observed. The energy dependence of the total transition-radiation intensity was studied using a radiator with large dimensions designed to yield energy-dependent signals at very high particle energies, up to E/mc-squared approximately equal to 100,000. The results are in good agreement with the theoretical predictions.

Cherry, M. L.↗
DOE OSTI2020

Sagnac fourier spectrometer (SAFOS)

A technique and device to determine the spectrum of electromagnetic radiation in a certain range of wavelengths comprising: splitting said radiation into more than one beam; let these beams counter-propagate in a Sagnac-type ring interferometer; and imprinting a wavelength-dependent angular tilt onto the wavefront of each beam by at least one dispersive element which preferably is a transmission grating or grism; and re-combining the multiple beams on a detector that exhibits spatial resolution and can therefore resolve the fringes formed by interference; and perform the mathematical operations to determine the spectrum of said radiation from the obtained interferogram, wherein the dispersive element is mounted on a stage providing linear and/or rotational movement.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1976

Impulsive solar X-ray bursts. 4: Polarization, directivity and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

A Monte Carlo method is described for evaluation of the spectrum, directivity and polarization of X-rays diffusely reflected from stellar photospheres. the accuracy of the technique is evaluated through comparison with analytic results. Using the characteristics of the incident X-rays of the model for solar X-ray flares, the spectrum, directivity and polarization of the reflected and the total X-ray fluxes are evaluated. The results are compared with observations.

Langer, S. H.↗
NASA NTRS1972

X-ray observations of pulsars.

The X-ray pulsations from NP 0532, discovered by Fritz et al. (1969), have been studied. The detectors in the investigations had wide fields of view, and the entire Crab Nebula NP 0532 radiation was detected. The power density spectrum of X-radiation observed is presented together with the shapes of X-ray and optical pulses. Searches for X-ray pulsations from other X-ray sources have also been carried out. The summarized results are shown in a table.

Bradt, H. V.↗