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Measured and Calculated Neutron Spectra and Dose Equivalent Rates at High Altitudes; Relevance to SST Operations and Space ResearchResults of the NASA Langley-New York University high-altitude radiation study are presented. Measurements of the absorbed dose rate and of secondary fast neutrons (1 to 10 MeV energy) during the years 1965 to 1971 are used to determine the maximum radiation exposure from galactic and solar cosmic rays of supersonic transport (SST) and subsonic jet occupants. The maximum dose equivalent rates that the SST crews might receive turn out to be 13 to 20 percent of the maximum permissible dose rate (MPD) for radiation workers (5 rem/yr). The exposure of passengers encountering an intense giant-energy solar particle event could exceed the MPD for the general population (0.5 rem/yr), but would be within these permissible limits if in such rare cases the transport descends to subsonic altitude; it is in general less than 12 percent of the MPD. By Monte Carlo calculations of the transport and buildup of nucleons in air for incident proton energies E of 0.02 to 10 GeV, the measured neutron spectra were extrapolated to lower and higher energies and for galactic cosmic rays were found to continue with a relatively high intensity to energies greater than 400 MeV, in a wide altitude range. This condition, together with the measured intensity profiles of fast neutrons, revealed that the biologically important fast and energetic neutrons penetrate deep into the atmosphere and contribute approximately 50 percent of the dose equivalant rates at SST and present subsonic jet altitudes.
Document ID
Document Type
Other - NASA Technical Note (TN)
Foelsche, T.
(NASA Langley Research Center Hampton, VA, United States)
Mendell, R. B.
(New York Univ. Hampton, VA, United States)
Wilson, J. W.
(NASA Langley Research Center Hampton, VA, United States)
Adams, R. R.
(NASA Langley Research Center)
Date Acquired
September 3, 2013
Publication Date
October 1, 1974
Subject Category
Space Radiation
Report/Patent Number
Accession Number
Funding Number(s)
PROJECT: RTOP 501-08-10-02
Distribution Limits
Work of the US Gov. Public Use Permitted.
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