Performance Study of Galactic Cosmic Ray Shield Materials

The use of trademarks or names of manufacturers in this report is for accurate reporting and does not constitute an ocial endorsement, either expressed or implied, of such products or manufacturers by the National Aeronautics and Space Administration. Summary The space program is faced with two dicult radiation protection issues for future long-term operations. First, retrot of shield material or conservatism in shield design is prohibitively expensive and often impossible. Second, shielding from the cosmic heavy ions is faced with limited knowledge on the physical properties and biological responses of these radiations. The current status of space shielding technology and its impact on radiation health is discussed herein in terms of conventional protection practice and a test biological response model. The impact of biological response on the selection of optimum materials for cosmic ray shielding is presented in terms of the transmission characteristics of the shield material. The transmission properties are, in turn, related to the nuclear cross sections of the cosmic heavy ions, for which an inadequate experimental database exists. Clearly, these physical and biological issues must be resolved before an adequate shield design can be dened. The choice of structural materials composition is a means of reducing astronaut exposure risk from space radiations in future NASA missions. The use of a performance index for shield materials related to the change in biological protection at constant shield mass and varying shield composition indicates performance indices up to a factor of 20. Although the sys-tematics of nuclear cross sections are able to demonstrate the relation of exposure risk to shield-material composition, the current uncertainty in nuclear cross sections will not allow an accurate evaluation of risk reduction. Even so, the unique role of hydrogenous materials used as high-performance shields is clear. Shinn et al. suggested that polyethylene with its short nuclear absorption lengths is an eective shield material in spite of the favoring of massive projectile fragments, and this is demonstrated herein for mono-energetic ion beams. This paper presents a theoretical study of risk-related factors and a pilot experiment to study the eectiveness of choice of shield materials to reduce the risk in space operations.