Assessment of Shielding Material Performance for Deep Space Missions
- PDF / 301,726 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 196 Views
NN8.10.1
Assessment of Shielding Material Performance for Deep Space Missions L. K. Mansur, B. J. Frame, N. C. Gallego, S. B. Guetersloh1, J. O. Johnson, J. W. Klett, and L. W. Townsend2 Oak Ridge National Laboratory Oak Ridge, Tennessee 37831-6138, USA 1 Lawrence Berkeley National Laboratory Berkeley, California 94720, USA 2 Nuclear Engineering Department, University of Tennessee Knoxville, Tennessee 37996-2300, USA ABSTRACT Radiation doses from galactic cosmic rays (GCR) are a significant issue for spacecraft crew exposures in deep space. We report initial work to evaluate a range of materials for GCR shielding. Earlier work has shown that conventional spacecraft materials, aluminum and higher atomic number structural alloys, provide relatively little shielding and, under certain conditions, may increase radiation risk. Materials containing high proportions of hydrogen and other low atomic mass nuclei provide improved GCR shielding. Polyethylene (PE) is generally considered a good performance benchmark shield material. However, PE shielding occupies volume and adds mass to the spacecraft. In this work we investigate several materials that are shown to provide shielding similar to PE, but which could furnish additional spacecraft functions, possibly eliminating the need for materials currently used for structural support or thermal management. Carbon forms that can incorporate a large mass of hydrogen, as well as polymers and polymer composites are being explored. Calculations of shielding effectiveness in GCR spectra have been carried out. Experiments to measure shielding properties recently have been completed at the NASA Space Radiation Laboratory (NSRL) located at Brookhaven National Laboratory (BNL) using high energy beans of O16. In this paper we report preliminary shielding results. INTRODUCTION Recent research on the effectiveness of spacecraft shielding materials in protecting human inhabitants during deep space missions has highlighted a strong need for new shielding technologies. Transport calculations for galactic cosmic rays (GCR), coupled with current models of biological effects have led to an understanding that conventional spacecraft materials like aluminum alloys do not provide adequate shielding. Under certain conditions, such materials could result in radiation effects more detrimental than for no shielding. Low Z materials, especially H but also elements up to C and O, offer significant improvements over Al in reducing biological dose [1-3]. Conventional models of biological effects are based on risk assessment dictated by the magnitude of linear energy transfer (LET) of an ion at a given energy, coupled with accepted quality factors that calibrate LET in terms of relative biological effectiveness (RBE) [4]. This dose equivalent approach is guided by the effect of X-rays in producing a certain effect, then relating the dose at which an energetic particle produces the same effect. Generally, the required particle dose is smaller. It is recognized, however, that heavy charged particles may inter
Data Loading...
