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  • ASTROPHYSICS  (1)
  • ATOMIC AND MOLECULAR PHYSICS  (1)
  • 1
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    In:  Other Sources
    Publication Date: 2019-06-27
    Description: Energetic particles can produce interstitial-vacancy pairs in a crystal by knocking the atoms from their normal positions. Detectors are unique among semiconductor devices in depending on very low concentrations of electrically active impurities, and also on efficient transport of holes and electrons over relatively large distances. Because the dense regions of damage produced by energetic particles may result in donors and/or acceptors, and also provide trapping sites for holes and electrons, detectors are very sensitive to radiation damage. In addition to these effects occurring within the detector, radiation may also change the characteristics of the exposed surfaces causing unpredictable effects on the detector leakage current. Radiation-induced surface degradation has rarely, if ever, been observed for germanium detectors. The possibility of minimizing hole trapping in charge collection by the use of a high-purity germanium coaxial detector configured with the p (+) contact on the coaxial periphery is discussed.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA. Goddard Space Flight Center Gamma Ray Spectry. in Astrophys.; p 473-478
    Format: text
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  • 2
    Publication Date: 2019-07-12
    Description: Results are reported from observations of the 511 MeV annihilation gamma-ray line from the Galactic center, made on May 22, 1989 with a high-resolution gamma-ray spectrometer on board a balloon launched from Alice Springs (Australia). The observations were made at about 4 gm/sq cm atmospheric depth for 6 hrs in a series of target and background pointings lasting 20 min each. The results obtained from multiparameter Gaussian fits to the data were as follows: 511 keV flux = 0.00089 + or - 0.00027 ph/sq cm per sec-rad, line width of about 1.1 keV, and less than 3.2 keV FWHM at 95 percent confidence.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 11; 8 19
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