Materials for High-Energy Radiation Shielding on Extra-Terrestrial Surfaces
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Materials for High-Energy Radiation Shielding on Extra-Terrestrial Surfaces R. L. Kiefer1, J. L. Chapman1, A. R. Boone1, and S. A. Thibeault2 Department of Chemistry, College of William and Mary, Williamsburg, VA 23187 2 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, VA 23681 ABSTRACT 1
Polyethylene and polypropylene were used with simulated lunar regolith to make microcomposites as possible materials for habitat construction on extra-terrestrial surfaces. The polymer powders were used in various mass percents and thoroughly mixed with regolith powder before heating. A heated press or a microwave oven was used to heat the polymer/regolith mixture and form the micro-composite. The resulting materials were characterized by thermal analysis. I. INTRODUCTION Radiation from galactic cosmic rays (GCR) and solar particle events (SPE) is a serious hazard to humans and electronic instruments during space travel, and during missions on extraterrestrial surfaces such as the Moon or Mars. Galactic cosmic radiation is composed of ~98% nucleons and ~2% electrons and positrons [1]. Although cosmic ray heavy ions are 1~2% of the fluence, these energetic heavy nuclei (HZE) contribute 50% of the long-term radiation dose [2]. Calculations have shown that HZE particles have a strong preference for interaction with light nuclei [3]. The best shield for this radiation would be liquid hydrogen, which is totally impractical. For this reason, hydrogen-containing polymers make the most effective practical shields. Long-term missions on the surface of the Moon or Mars will require the construction of habitats to protect humans during their stay. One approach to the construction is to make structural materials from lunar or Martian regolith using a polymeric material as a binder. The hydrogen-containing polymers are considerably more effective for radiation protection than the regolith alone [4], but the combination minimizes the amount of polymer to be transported. We have made microcomposites of simulated lunar regolith with polyethylene (PE) and polypropylene (PP) using a heated press or an easily transportable microwave oven. Both polyethylene and polypropylene have an empirical formula of CH2 which is the maximum hydrogen content of any polymer. Specimens were characterized using thermogravimetric analysis (TGA) and thermomechanical analysis (TMA) for samples made in both the heated press and the microwave oven. II. EXPERIMENTAL Sample Preparation Simulated lunar regolith was mixed individually with two different polymers, reversed phase high-performance liquid chromatographic (HPLC) grade polyethylene, and HPLC grade polypropylene. The simulant resembles surface materials from the Apollo 11 site on the Moon and is purchased from the Department of Geology and Geophysics at the University of
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Minnesota, Twin Cities. It is made by crushing, grinding, and sieving 1.1 billion year old basaltic rock from Minnesota. Both polymers were purchased from Polysciences, Inc and were used as receive
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