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  • Other Sources  (9)
  • SPACE RADIATION
  • General Chemistry
  • Cell & Developmental Biology
  • 1995-1999  (9)
  • 1970-1974
  • 1996  (9)
  • 1
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    Shielding against galactic cosmic rays (1996)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Ions of galactic origin are modified but not attenuated by the presence of shielding materials. Indeed, the number of particles and the absorbed energy behind most shield materials increases as a function of shield thickness. The modification of the galactic cosmic ray composition upon interaction with shielding is the only effective means of providing astronaut protection. This modification is intimately conntected with the shield transport porperties and is a strong function of shield composition. The systematic behavior of the shield properites in terms of microscopic energy absorption events will be discussed. The shield effectiveness is examined with respect to convectional protection practice and in terms of a biological endpoint: the efficiency for reduction of the probability of transformation of shielded C3H1OT1/2 mouse cells. The relative advantage of developing new shielding technologies is discussed in terms of a shield performance as related to biological effect and the resulting uncertainty in estimating astronaut risk.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)31-(2)36
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    NASA TECHNICAL REPORTS
  • 2
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    Decay rate of the second radiation belt (1996)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Variations in the Earth's trapped (Van Allen) belts produced by solar flare particle events are not well understood. Few observations of increases in particle populations have been reported. This is particularly true for effects in low Earth orbit, where manned spaceflights are conducted. This paper reports the existence of a second proton belt and it's subsequent decay as measured by a tissue-equivalent proportional counter and a particle spectrometer on five Space Shuttle flights covering an eighteen-month period. The creation of this second belt is attributed to the injection of particles from a solar particle event which occurred at 2246 UT, March 22, 1991. Comparisons with observations onboard the Russian Mir space station and other unmanned satellites are made. Shuttle measurements and data from other spacecraft are used to determine that the e-folding time of the peak of the second proton belt. It was ten months. Proton populations in the second belt returned to values of quiescent times within eighteen months. The increase in absorbed dose attributed to protons in the second belt was approximately 20%. Passive dosimeter measurements were in good agreement with this value.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)151-158
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    NASA TECHNICAL REPORTS
  • 3
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    Overview of nuclear fragementation models and needs (1996)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: It has been known for some time that adequate assessment of spacecraft requirements and concomitant estimates of astronaut radiation exposures from galactic cosmic radiation requires accurate, quantitative methods for characterizing these radiation fields as they pass through thick absorbers. The main nuclear interaction processes involved are nuclear elastic an inelastic collisions, and nuclear breakup (fragmentation) and electromagnetic dissociation (EMD). Nuclear fragmenation and EMD are important because they alter the elemental and isotopic composition of the transported radiation fields. At present, there is no suitable accurate theory for predicting nuclear fragmentation cross sections for all collision pairs and energies of interest in space radiation protection. Typical cross-section differences between theory and experiment range from about 25 percent to a factor of two. The resulting errors in transported flux, for high linear energy transfer (LET) particles, are compared to these cross-sections errors. In this overview, theoretical models of heavy ion fragmentation currently used to generate input data bases for cosmic-ray transport and shielding codes are reviewed. Their shortcomings are discussed. Further actions needed to improve their accuracy and generality are presented.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)59-(2)68
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    NASA TECHNICAL REPORTS
  • 4
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    Near-Earth Radiation Environment Including Time Variations and Secondary Radiation; Meetings F2.6 and F2.7, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994 (1996)
    In:  Other Sources
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    Publication Date: 2019-03-30
    Description: Both man and technological equipment must survive the near-earth space radiation environment, which can, under specific conditions, be extremely severe. This conference produced 17 papers on the dynamic space radiation environment covering: galactic, solar and trapped particles; nuclear fragmentation; nuclear interactions and transport theory; solar proton events; radiation shielding; and heavy ion fluences. Several papers present results from the recent SAMPEX mission.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2
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  • 5
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    Theoretical model of HZE particle fragmentation by hydrogen targets (1996)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: The fragmenting of high energy, heavy ions (HZE particles) by hydrogen targets is an important, physical process in several areas of space radiation research. In this work quantum mechanical optical model methods for estimating cross sections for HZE particle fragmentation by hydrogen targets are presented. The cross sections are calculated using a modified abrasion-ablation collision formalism adapted from a nucleus-nucleus collision model. Elemental and isotopic production cross sections are estimated and compared with reported measurements for the breakup of neon, sulphur, and iron, nuclei at incident energies between 400 and 910 Mev/nucleon. Good agreement between theory and experiment is obtained.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)109-(2)112
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  • 6
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    Light ion components of the galactic cosmic rays: Nuclear interactions and transport theory (1996)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Light nuclei are present in the primary galactic cosmic rays (GCR) and are produced in thick targets due to projectile or target fragmentation from both nucleon and heavy induced reactions. In the primary GCR, He-4 is the most abundant nucleus after H-1. However, there are also a substantial fluxes of H-2 and He-3. In this paper we describe theoretical models based on quantum multiple scattering theory for the description of light ion nuclear interactions. The energy dependence of the light ion fragmentation cross section is considered with comparisons of inclusive yields and secondary momentum distributions to experiments described. We also analyze the importance of a fast component of lights ions from proton and neutron induced target fragementation. These theoretical models have been incorporated into the cosmic ray transport code HZETRN and will be used to analyze the role of shielding materials in modulating the production and the energy spectrum of light ions.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)77-(2)86
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  • 7
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    Galactic cosmic radiation model and its applications (1996)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: A model for the differential energy spectra of galactic cosmic radiation as a function of solar activity is described. It is based on the standard diffusion-convection theory of solar modulation. Estimates of the modulation potential based on fitting this theory to observed spectral measurements from 1954 to 1989 are correlated to the Climax neutron counting rates and to the sunspot numbers at earlier times taking into account the polarity of the interplanetary magnetic field at the time of observations. These regression lines then provide a method for predicting the modulation at later times. The results of this model are quantitatively compared to a similar Moscow State University (MSU) model. These model cosmic ray spectra are used to predict the linear energy transfer spectra, differential energy spectra of light (charge less than or = 2) ions, and single event upsets rates in memeory devices. These calculations are compared to observations made aboard the Space Shuttle.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)7-(2)17
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    NASA TECHNICAL REPORTS
  • 8
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    Geomagnetic transmission disturbances and heavy-ion fluences observed in low Earth orbit during the solar energetic particle events of October 1989 (1996)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The large solar energetic particle (SEP) events and simultaneous large geomagnetic disturbances observed during October 1989 posed a significant, rapidly evolving space radiation hazard. Using data from the GOES-7, NOAA-10, IMP-8 and LDEF satellites, we determined the geomagnetic transmission, heavy ion fluences, mean Fe ionic charge state, and effective radiation hazard observed in low Earth orbit (LEO) for these SEPs. We modeled the geomagneitc transmission by tracing particles through the combination to the internal International Geomagnetic Reference Field (IGRF) and the Tsyganenko (1989) magnetospheric field models, extending the modeling to large geomagnetic disturbances. We used our results to assess the radiation hazard such very large SEP events would pose in the anticipated 52 deg inclination space station orbit.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)121-(2)125
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    NASA TECHNICAL REPORTS
  • 9
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    LET spectra of trapped anomalous cosmic rays in low-Earth orbit (1996)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Observations aboard Cosmos satelites discovered trapped anomalous cosmic rays (ACRs), tracked the variation in their intensity in 1986-1988, and measured their fluence, spectrum, and composition at solar minimum in the previous solar cycle. The MAST instrument aboard the SAMPEX satellite has observed trapped anomalous cosmic rays in the present solar cycle, confirmed the general features of the Cosmos data, and provided the first detailed observations of trapped ACRs. In this paper we apply theoretical modeling of trapped ACRs, which is shown to provide a reasonably good description of both the Cosmos and SAMPEX data, to calculate the integral linear-energy-transfer (LET) spectra due to trapped ACRs in typical low-Earth orbits. We compare these calculations with the LET spectra produced by galactic cosmic rays (GCRs) and non-trapped ACRs in order to assess the relative radiation hazard posed by trapped ACRs.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 17; 2; p. (2)47-(2)51
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