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  • 1
    Electronic Resource
    Electronic Resource
    Issues in protection from galactic cosmic rays (1995)
    Springer
    Radiation and environmental biophysics 34 (1995), S. 217-222 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Radiation risks to astronauts depend on the microscopic fluctuations of energy absorption events in specific tissues. These fluctuations depend not only on the space environment but also on the modifications of that environment by the shielding provided by structures surrounding the astronauts and the attenuation characteristics of the astronaut's body. The effects of attenuation within the shield and body depends on the tissue biological response to these microscopic fluctuations. In the absence of an accepted method for estimating astronaut risk, we examined the attenuation characteristics using conventional linear energy transfer (LET)-dependent quality factors (as one means of representing relative biological effectiveness, RBE) and a track-structure repair model to fit cell transformation (and inactivation) data in the C3H10 T1/2 mouse cell system obtained for various ion beams. Although the usual aluminum spacecraft shield is effective in reducing dose equivalent with increasing shield thickness, cell transformation rates are increased for thin aluminum shields. Clearly, the exact nature of the biological response to LET and track width is critical to evaluation of biological protection factors provided by a shield design. A significant fraction of biological injury results from the LET region above 100 keV/µm. Uncertainty in nuclear cross-sections results in a factor of 2–3 in the transmitted LET spectrum beyond depths of 15 g/cm2, but even greater uncertainty is due to the combined effects of uncertainty in biological response and nuclear parameters. Clearly, these uncertainties must be reduced before the shield design can be finalised.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01209745
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A Green's function method for heavy ion beam transport (1995)
    Springer
    Radiation and environmental biophysics 34 (1995), S. 155-159 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abtract The use of Green's function has played a fundamental role in transport calculations for high-charge high-energy (HZE) ions. Two recent developments have greatly advanced the practical aspects of implementation of these methods. The first was the formulation of a closedform solution as a multiple fragmentation perturbation series. The second was the effective summation of the closedform solution through nonperturbative techniques. The nonperturbative methods have been recently extended to an inhomogeneous, two-layer transport media to simulate the lead scattering foil present in the Lawrence Berkeley Laboratories (LBL) biomedical beam line used for cancer therapy. Such inhomogeneous codes are necessary for astronaut shielding in space. The transport codes utilize the Langley Research Center atomic and nuclear database. Transport code and database evaluation are performed by comparison with experiments performed at the LBL Bevalac facility using 670A MeV20Ne and 600A MeV56Fe ion beams. The comparison with a time-of-flight and ΔE detector measurement for the20Ne beam and the plastic nuclear track detectors for56Fe show agreement up to 35%–40% in water and aluminium targets, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01211542
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  • 3
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    Nonperturbative methods in HZE propagation (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An analytical solution to the perturbative multiple collision series of a fragmenting HZE ion beam has limited usefulness since the first collision term has several hundred contributions, the second collision term has tens of thousands of contributions, and each successive collision term progresses to unwieldy computational proportions. Our previous work has revealed the multiple collision terms in the straight-ahead approximation to be simple products of a spatially dependent factor times a linear energy-dependent factor of limited domain and unit normalization. The properties of these forms allow the development of the nonperturbative summation of the series to all orders assuming energy-independent nuclear cross sections as matrix products of a scaled Green's function described herein. This nonperturbative Green's function with multiple scattering correction factors compares well with experiments using 670 MeV/u neon-20 ion beams in thick water targets.
    Keywords: Life Sciences (General)
    Type: Radiation research (ISSN 0033-7587); Volume 140; 2; 241-8
    Format: text
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  • 4
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    Implication of microdosimetry in estimation of radiation quality in space environment (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Errors introduced using a tissue equivalent proportional counter to estimate radiation quality of an arbitrary ion field as related to space radiations are examined. This is accomplished by using a generalized analytic model to calculate the effect of energy loss straggling, track structure, and pathlength distribution on the microdosimetric distribution. The error can be as large as a factor of two, but no systematic trend could be found.
    Keywords: Life Sciences (General)
    Type: Health physics (ISSN 0017-9078); Volume 76; 5; 510-5
    Format: text
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  • 5
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    Effects of target fragmentation on evaluation of LET spectra from space radiations: implications for space radiation protection studies (1996)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We present calculations of linear energy transfer (LET) spectra in low earth orbit from galactic cosmic rays and trapped protons using the HZETRN/BRYNTRN computer code. The emphasis of our calculations is on the analysis of the effects of secondary nuclei produced through target fragmentation in the spacecraft shield or detectors. Recent improvements in the HZETRN/BRYNTRN radiation transport computer code are described. Calculations show that at large values of LET (〉 100 keV/micrometer) the LET spectra seen in free space and low earth orbit (LEO) are dominated by target fragments and not the primary nuclei. Although the evaluation of microdosimetric spectra is not considered here, calculations of LET spectra support that the large lineal energy (y) events are dominated by the target fragments. Finally, we discuss the situation for interplanetary exposures to galactic cosmic rays and show that current radiation transport codes predict that in the region of high LET values the LET spectra at significant shield depths (〉 10 g/cm2 of Al) is greatly modified by target fragments. These results suggest that studies of track structure and biological response of space radiation should place emphasis on short tracks of medium charge fragments produced in the human body by high energy protons and neutrons.
    Keywords: Aerospace Medicine
    Type: Radiation measurements (ISSN 1350-4487); Volume 26; 6; 923-34
    Format: text
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  • 6
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    An analysis of energy deposition in a tissue equivalent proportional counter onboard the space shuttle (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An improved prediction for space radiations in the lower earth orbits measured by the shuttle TEPC is obtained when energy loss straggling and chord length distribution of the detector are considered. A generalized analytic model is used to describe the energy deposition of direct ion interaction events in a micron-size detector. The transport calculation accounting for the shuttle configuration is accomplished by using a new version of HZETRN that has been extensively verified with laboratory and flight data. The agreement of predicted and measured lineal energy spectra is within 70% for the region above 2 keV/micrometer but within a factor of 2.3 underpredicted for the region below this value. The inclusion of indirect delta ray events in the model is needed before possible causes for the underprediction below 2 keV/micrometer can be assessed.
    Keywords: Life Sciences (General)
    Type: Radiation measurements (ISSN 1350-4487); Volume 30; 1; 19-28
    Format: text
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  • 7
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    Galactic cosmic ray transport methods and radiation quality issues (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An overview of galactic cosmic ray (GCR) interaction and transport methods, as implemented in the Langley Research Center GCR transport code, is presented. Representative results for solar minimum, exo-magnetospheric GCR dose equivalents in water are presented on a component by component basis for various thicknesses of aluminum shielding. The impact of proposed changes to the currently used quality factors on exposure estimates and shielding requirements are quantified. Using the cellular track model of Katz, estimates of relative biological effectiveness (RBE) for the mixed GCR radiation fields are also made.
    Keywords: SPACE RADIATION
    Type: International Journal of Radiation Applications and Instrumentation, Part D: Nuclear Tracks and Radiation Measurements (ISSN 0735-245X); 20; 1; p. 65-72.
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  • 8
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    Track structure model for damage to mammalian cell cultures during solar proton events (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Solar proton events (SPEs) occur infrequently and unpredictably, thus representing a potential hazard to interplanetary space missions. Biological damage from SPEs will be produced principally through secondary electron production in tissue, including important contributions due to delta rays from nuclear reaction products. We review methods for estimating the biological effectiveness of SPEs using a high energy proton model and the parametric cellular track model. Results of the model are presented for several of the historically largest flares using typical levels and body shielding.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: International Journal of Radiation Applications and Instrumentation, Part D: Nuclear Tracks and Radiation Measurements (ISSN 0735-245X); 20; 1; p. 177-184.
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  • 9
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    Human exposure to galactic cosmic rays in space (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The Langley Research Center GCR (galactic cosmic rays) code (HZETRN) and the computerized Anatomical Man (CAM) model are used to estimate astronaut exposures, from GCR particles, for missions beyond earth's magnetosphere. Conventional risk assessments in terms of total absorbed dose and dose equivalent are made for skin, ocular lens, and bone marrow. For each organ, evaluations are made of relative contributions from incident protons, iron nuclei, and their secondary reaction products.
    Keywords: MAN/SYSTEM TECHNOLOGY AND LIFE SUPPORT
    Type: ; : Strong shock waves
    Format: text
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  • 10
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    Issues in protection from galactic cosmic rays (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Radiation risks to astronauts depend on the microscopic fluctuations of energy absorption events in specific tissues. These fluctuations depend not only on the space environment but also on the modifications of that environment by the shielding provided by structures surrounding the astronauts and the attenuation characteristics of the astronaut's body. The effects of attenuation within the shield and body depends on the tissue biological response to these microscopic fluctuations. In the absence of an accepted method for estimating astronaut risk, we examined the attenuation characteristics using conventional linear energy transfer (LET)-dependent quality factors (as one means of representing relative biological effectiveness, RBE) and a track-structure repair model to fit cell transformation (and inactivation) data in the C3H10 T1/2 mouse cell system obtained for various ion beams. Although the usual aluminum spacecraft shield is effective in reducing dose equivalent with increasing shield thickness, cell transformation rates are increased for thin aluminum shields. Clearly, the exact nature of the biological response to LET and track width is critical to evaluation of biological protection factors provided by a shield design. A significant fraction of biological injury results from the LET region above 100 keV/mu m. Uncertainty in nuclear cross-sections results in a factor of 2-3 in the transmitted LET spectrum beyond depths of 15 g/cm2, but even greater uncertainty is due to the combined effects of uncertainty in biological response and nuclear parameters. Clearly, these uncertainties must be reduced before the shield design can be finalised.
    Keywords: Aerospace Medicine
    Type: Radiation and environmental biophysics (ISSN 0301-634X); Volume 34; 4; 217-22
    Format: text
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