Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Background radiation”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Pregalactic black holes - A new constraint

Pregalactic black holes accrete matter in the early universe and produce copious amounts of X radiation. By using observations of the background radiation in the X and gamma wavebands, a strong constraint is imposed upon their possible abundance. If pregalactic black holes are actually present, several outstanding problems of cosmogony can be resolved with typical pregalactic black hole masses of 100 solar masses. Significantly more massive holes cannot constitute an appreciable mass fraction of the universe and are limited by a specific mass-density bound.

Barrow, J. D.↗
NASA NTRS1992

TeV gamma rays from 3C 279 - A possible probe of origin and intergalactic infrared radiation fields

The gamma-ray spectrum of 3C 279 during 1991 June exhibited a near-perfect power law between 50 MeV and over 5 GeV with a differential spectral index of -(2.02 +/- 0.07). If extrapolated, the gamma-ray spectrum of 3C 279 should be easily detectable with first-generation air Cerenkov detectors operating above about 0.3 TeV provided there is no intergalactic absorption. However, by using model-dependent lower and upper limits for the extragalactic infrared background radiation field, a sharp cutoff of the 3C 279 spectrum is predicted at between about 0.1 and about 1 TeV. The sensitivity of present air Cerenkov detectors is good enough to measure such a cutoff, which would provide the first opportunity to obtain a measurement of the extragalactic background infrared radiation field.

Stecker, F. W.↗
NASA NTRS1976

Reanalysis of the Apollo cosmic gamma-ray spectrum in the 0.3 to 10 MeV energy region

Additional data obtained from the Apollo-16 and -17 missions, together with collateral calculations on background radiation effects, have enabled an improved subtraction of unwanted backgrounds from the diffuse cosmic gamma-ray data previously reported from Apollo-15. As a result, the 1- to 10-MeV spectrum is lowered significantly and connects smoothly with recent data at other energies. The inflection reported previously is much less pronounced and has no more than a 1.5-sigma significance. Sky occultation by the Apollo-16 spacecraft shows the bulk of the 0.3- to 1-MeV radiation to be diffuse. The analysis of spurious backgrounds points to important improvements for future experiments designed for this spectral region.

Trombka, J. I.↗
NASA NTRS1982

Neutrino masses, neutrino oscillations, and cosmological implications

Theoretical concepts and motivations for considering neutrinos having finite masses are discussed and the experimental situation on searches for neutrino masses and oscillations is summarized. The solar neutrino problem, reactor, deep mine and accelerator data, tri decay experiments and double beta-decay data are considered and cosmological implications and astrophysical data relating to neutrino masses are reviewed. The neutrino oscillation solution to the solar neutrino problem, the missing mass problem in galaxy halos and galaxy cluster galaxy formation and clustering, and radiative neutrino decay and the cosmic ultraviolet background radiation are examined.

Stecker, F. W.↗
NASA NTRS1996

Bolometric detector systems for IR and mm-wave space astronomy

Recent developments in bolometric detector systems for millimeter and submillimeter wave space astronomy are described. Current technologies meet all the requirements for the high frequency instrument onboard the cosmic background radiation anisotropy satellite/satellite for the measurement of background anisotropies (COBRAS/SAMBA) platform. It is considered that the technologies that are currently being developed will significantly reduce the effective time constant and/or the cooling requirements of bolometric detectors. These technologies lend themselves to the fabrication of the large format arrays required for the Far Infrared and Submillimeter Space Telescope (FIRST). The scientific goals and detector requirements of the COBRAS/SAMBA platform that will use infrared bolometers are reviewed and the baseline detector system is described, including the feed optics, the infrared filters, the cold amplifiers and the warm readout electronics.

Church, S. E.↗
NASA NTRS1983

Decay of long-lived particles in the early universe

It is pointed out that radiative decay of massive fermions can distort the cosmic background radiation. The present investigation is concerned with a study of decay lifetimes in the range from 10 to 100,000 years. Attention is given to the physics involved in determining the effect of radiative decay of massive fermions on observed photon backgrounds. The case of particles which decoupled when the effective number of species in equilibrium was in the range from 50 to 100 is considered, and constraints on particle masses and lifetimes are placed on the basis of observed photon fluxes. This approach provides results with special applications to particles predicted by supersymmetry theories and to right-handed neutrinos. Implications for galaxy formation are also discussed.

Silk, J.↗
NASA NTRS1989

Galaxy formation by mock gravity with dust?

Absorbing dust immersed in an isotropic radiation field experiences an attractive force, 'mock gravity', due to mutual shadowing, and the resulting mock gravitational instability can lead to clumping of dust and gas. The effects of mock gravity in the pre-Galactic universe are studied here, including imcomplete coupling of dust and gas, finite gas pressure, radiative drag both by the radiation that causes the instability and by the cosmic microwave background radiation, and finite albedo of dust, all of which have been neglected in the previous calculations. It is concluded that the radiation field implied by the submillimeter background is not strong enough to cause clumping of gas on scales of interest.

Wang, Boqi↗
NASA NTRS1987

In situ measurement of atomic hydrogen in the upper mesosphere

In situ measurements of H abundance between 73 and 93 km are reported for conditions of winter solstice, magnetic quiet, and a solar depression angle of 12 deg. The data were obtained by a rocket-borne instrument using the resonance fluorescence technique. A discharge source emitting photons at 1216 A was an integral part of the instrument. The instrument was radially deployed 80 cm by a boom from the front of the payload in order to avoid the shock created by the gas flow over the front of the payload. An attitude control system oriented the payload so that the gas flow was nearly perpendicular to the plane containing the incident and scattered photons, thus minimizing any correction for Doppler shift. The resonance radiation detector viewed a black backstop in order to minimize background radiation from the hydrogen geocorona; however, the background was not entirely eliminated. The signal-to-noise ratio was improved by summing the data in 1.8-s bins. The observed hydrogen concentration maximized at 85 km at 1.5 + or - 1.1 x 10 to the 8th atoms/cu cm.

Sharp, W. E.↗
NASA NTRS1977

Reanalysis of the Apollo cosmic gamma-ray spectrum in the 0.3 to 10 MeV energy region

Additional data obtained from the Apollo 16 and 17 missions, together with collateral calculations on background radiation effects, have made possible an improved subtraction of unwanted backgrounds from the diffuse cosmic gamma ray data previously reported from Apollo 15. As a result, the 1 to 10 MeV spectrum is lowered significantly and connects smoothly with recent data at other energies. The inflection reported previously is much less pronounced and has no more than 1.5 sigma significance. Sky occultation by the Apollo 16 spacecraft shows the bulk of the 0.3 to 1 MeV radiation to be diffuse. The analysis of spurious backgrounds points to important improvements for future experiments designed for this spectral region. A light-weight satellite design can give a fourfold improvement in the signal to noise for such a measurement. Use of an anisotropic central crystal, which spins quickly compared with possible time variations in detector background, would enable sensitive limits to be set on galactic plane and point source contributions.

Dyer, C. S.↗
NASA NTRS1977

Reanalysis of the Apollo cosmic gamma-ray spectrum in the 0.3 to 10 MeV energy region

Additional data obtained from the Apollo 16 and Apollo 17 missions, together with collateral calculations on background radiation effects, have made possible an improved subtraction of unwanted backgrounds from the diffuse cosmic gamma-ray data previously reported from Apollo 15. As a result, the 1- to 10-MeV spectrum is lowered significantly and connects smoothly with recent data at other energies. The inflection reported previously is much less pronounced and has no more than a 1.5-sigma significance. Sky occultation by the Apollo 16 spacecraft shows the bulk of the 0.3- to 1-MeV radiation to be diffuse. The analysis of spurious backgrounds points to important improvements for future experiments designed for this spectral region.

Trombka, J. I.↗
NASA NTRS1982

On the contribution of a stochastic background of gravitational radiation to the timing noise of pulsars

The influence of a stochastic and isotropic background of gravitational radiation on timing measurements of pulsars is investigated, and it is shown that pulsar timing noise may be used to establish a significant upper limit of about 10 to the -10th on the total energy density of very long-wavelength stochastic gravitational waves. This places restriction on the strength of very long wavelength gravitational waves in the Friedmann model, and such a background is expected to have no significant effect on the approximately 3 K electromagnetic background radiation or on the dynamics of a cluster of galaxies.

Mashhoon, B.↗
NASA NTRS2004

Validating Lidar Depolorization Calibration using Solar Radiation Scattered by Ice Clouds

This letter proposes the use of solar background radiation scattered by ice clouds for validating space lidar depolarization calibration. The method takes advantage of the fact that the background light scattered by ice clouds is almost entirely unpolarized. The theory is examined with Cloud Physics Lidar (CPL) background light measurements.

Liu, Zhao-Yang↗
NASA NTRS1967

Training course for radiation safety technicians

Course of instruction includes sections on basic information, natural radioactivity, properties of alpha, beta, gamma, X rays, and neutrons, concepts of radiation units and dose determinations, shielding, biological effects, background radiation, radiation protection standards, and internal dose calculation.

Lasuk, S. R.↗
NASA NTRS1994

The blazar gamma-ray luminosity function and the diffuse extragalactic gamma-ray background

We have used the data from the new EGRET catalog on 'grazars' (blazers which are observed to be high-energy gamma-ray sources), together with radio data, to construct a new relation between radio and gamma-ray luminosity for these sources. Using this relation to construct a grazar gamma-ray luminosity function, we then calculate the contribution of unresolved grazars to the cosmic gamma-ray background radiation. We derive the energy spectrum of this background component above 100 MeV and the angular fluctuations in this background implied by our model.

Salamon, M. H.↗
NASA NTRS1992

He I absorption by Lyman-alpha clouds and low-redshift Lyman-alpha clouds

Sources and sinks of radiation are used to model the evolution of the metagalactic ionizing background radiation field. It is shown that, if the comoving number density of quasars approached constancy at high redshift, as suggested by some recent observations, the observed ionizing background might possibly have been produced by the observed quasars alone. Consideration is also given to the UV radiation from decaying neutrons proposed by Sciama (1990), as an extra possible source. If is found that, if the background spectrum were as soft as in the Sciama scenario, the observed Ly-alpha clouds would contain detectable amounts of neutral helium, producing an 'He I forest' almost as dense as the hydrogen forest, due to the 584-A transition 1s-squared-1s2p. It is argued that observations of the Ly-alpha forest contradict the Sciama hypothesis.

Miralda-Escude, Jordi↗
NASA NTRS1991

Spectral observations of the extreme ultraviolet background

The design of a grazing incidence spectrometer for measuring the diffusive extreme-ultraviolet astronomical background radiation is outlined, and the data obtained on the diffusive background between 80 and 650 A is discussed. The strongest emission line detected is solar backscattered He I 584 A radiation; solar 304 A radiation resonantly scattered by geocoronal He II is observed in both first and second order; and each of three remaining spectral features is found to be consistent with those expected from hot interstellar gas. Of these features, the strongest is the feature at 635 A identified as 630 A O v emission. A feature centered at about 99 A is fitted by a cluster of Fe XVIII and Fe XIX lines from gas at log T = 6.6-6.8, and a feature discovered near 178 A is found to be consistent with Fe X and Fe XI emission from gas at log T = 6.

Labov, Simon E.↗
NASA NTRS1981

Dipole and quadrupole anisotropy of the 2.7 K radiation

Results of measurements of the dipole and quadrupole anisotropy of the microwave background radiation are reported. Balloon-borne measurements of the temperature difference between two horn antennas pointed 90 deg apart and 45 deg from the zenith were carried out at frequencies of 24.8, 31.4 and 46.0 GHz to determine three dipole and four quadrupole parameters. When combined with data from two previous balloon flights, a dipole anisotropy of 3.78 + or - 0.30 mK in the direction 11.6 + or - 0.2 h RA, -12 + or - 5 deg dec is obtained. The measurements reveal a spectral index of 0.04 + or - 0.28 between 19.0 and 46.0 GHz, indicating that the dipole effect arises from an intrinsic anisotropy in the temperature of the background and/or a first-order Doppler shift due to solar motions. A statistically significant quadrupole effect is also detected which is attributed to the intrinsic anisotropy of the 2.7 K background.

Boughn, S. P.↗