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  • Other Sources  (16)
  • 11
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    A coded aperture gamma ray telescope (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A gamma ray telescope is being developed to operate in the energy range 100 keV to 5 MeV, utilizing coded aperture imaging. The design incorporates a mask pattern based on a Uniformly Redundant Array (URA), which has been shown to have ideal imaging characteristics. A mask-anti-mask procedure is used to eliminate the effects of any possible systematic variations in detector background rates. The detector array is composed of 35 elements of the high-Z material Bismuth Germanate (BGO). Results of laboratory testing of the imaging properties will be presented. A southern hemisphere balloon flight is planned for 1982 with the goal of observing the 0.511 MeV radiation from the Galactic Center. Computer calculations show that a point source of this radiation can be located to within + or - 1 deg.
    Keywords: ASTRONOMY
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    NASA TECHNICAL REPORTS
  • 12
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    Gamma-ray observations of Cygnus X-1 and Cygnus X-3 using a coded-aperture telescope (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A balloon-borne coded-aperture telescope, measuring gamma-ray photons in the 160 keV to 9.3 MeV range, was used to observe the Cygnus region of the sky on October 1 and 2, 1984. In the 2-9.3-MeV band, evidence is found for a hard spectral component with a mean flux level at the top of the atmosphere of 7.4 + or - 2.5 x 10 to the -7th photons/sq cm per s per keV, inconsistent with the predictions of the inverse Compton models normally used to describe the X-ray emission. Both Cyg X-1 and Cyg X-3 could be observed simultaneously with the telescope. The results are used to establish 1-sigma upper flux limits on the spectral emission from Cyg X-3.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 343; 317-322
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  • 13
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    Gamma-rays and neutrons as a probe of the proton spectrum during the solar flare of 1988 December 16 (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We have previously reported on high-energy gamma-rays and neutrons from the flare of 1988 December 16 detected by the Gamma-Ray Spectrometer on the SMM satellite. In this paper, we present results on gamma-ray lines seen by the same detector during this flare. Together, these measurements constitute a powerful probe of the proton spectrum that produces the flare neutrals. Analysis of the data suggests a Bessel-function proton spectrum with a shape parameter (alpha T) of 0.054 +/- 0.004 and the number of protons above 30 MeV equal to (9.0 +/- 0.9) x 10 exp 32. The number of neutrons detected from this flare is much smaller than what is predicted from an isotropic distribution of the protons, indicating that the distribution may be nonisotropic.
    Keywords: SOLAR PHYSICS
    Type: In: Particle acceleration in cosmic plasmas; Proceedings of the Workshop, Bartol Research Inst., Newark, DE, Dec. 4-6, 1991 (A93-39976 16-93); p. 253-256.
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  • 14
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    Effects of line width and spatial extent on measurements of the 0.51 MeV Galactic center line (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Over the past 15 years, a number of measurements have been made of positron-electron annihilation radiation from the Galactic Center region. The results after 1979 show a significant decrease in measured flux intensity from that previously observed with the same instruments. This is probably due to time variations; however, the contributions of a spatially extended and/or energy-broadened component should also be considered. The entire data set is consistent with a time variable point source plus a distribution along the Galactic Disk. There is no strong evidence for a component broadened in energy.
    Keywords: ASTROPHYSICS
    Type: Positron-electron pairs in astrophysics; Jan 06, 1983 - Jan 08, 1983; Greenbelt, MD
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  • 15
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    Gamma-ray observations of the Crab Region using a coded-aperture telescope (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The region of the Galactic anticenter, including the Crab Nebula, was observed during a balloon flight of the University of New Hampshire Directional Gamma-Ray Telescope employing the coded-aperture imaging technique to image celestial gamma-radiation between 160 keV and 9.3 MeV. The background systematics are treated with a simple and relatively straightforward correction procedure. The results demonstrate that the coded-aperture procedure is a viable approach for imaging not only point sources of radiation, but also extended sources of emission. The results for the Crab's photon spectrum are consistent with a power-law spectrum. Upper limits on the flux levels of line emission at 405 keV and 1050 keV and on the flux from the X-ray binary source A0535 + 26 and diffuse Galactic emission from the anticenter region are derived.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 321; 543-552
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  • 16
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    Accelerator measurement of NaI response to medium energy neutrons and application to a satellite-borne spectrometer (1992)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: We report on the response of a prototype detector to medium energy neutrons. The neutrons were produced by n-p scattering of a neutron beam on a hydrogen target. The measurements provide unique data on the efficiency and response of large NaI scintillators to neutrons in the energy range 36-709 MeV. We apply the results to the high-energy mode of the Gamma-Ray Spectrometer (GRS) on the Solar Maximum Mission satellite by estimating its efficiency for neutron detection. This estimate is compared to earlier Monte Carlo calculations of the GRS efficiency.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Experimental Astronomy (ISSN 0922-6435); 2; 4; p. 233-258.
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