They found that, ideally, PE as the low-Z material in this composite should be at the surface layer and interact firstly with the incident radiation, in this way enabling the building of a multi-layer composite from PE and graphite which gives better radiation shielding, as simulated with a particle transport simulation code, taking into account solar particles, cosmic rays, protons, and electrons along the highly elliptical orbit. While pure graphite alone has better shielding properties than the often used aluminum, its mechanical properties are insufficient, resulting in the necessity to improve them by adding materials with higher atomic number. Ĭombining graphite fibers with polyethylene (PE), Emmanuel and Raghavan investigated the possibility of preparing optimized shields for highly elliptical orbit satellites. prepared composites from carbon-fiber-reinforced epoxy composites with or without BN nanoparticles and found a positive impact on the mechanical properties of the composites even for small amounts of BN nanoparticles. With a similar technique, Ghazizadeh et al. Introducing the same nanoparticles into high-molecular-weight polyethylene/epoxy composites resulted in more than 99% shielding performance for all sandwich panels, with boron nanopowder showing the highest radiation-shielding efficiency, as tested with thermalized neutrons and measured by the transmitting neutron flow through the sample. Producing sandwich panels by vacuum-assisted resin transfer molding, they found more than 99% shielding of these composites against neutron irradiation, while the core materials maintained their mechanical and thermo-physical properties after the radiation experiments. used another approach and combined boron and boron carbide nanoparticles as well as gadolinium nanoparticles with UHMWPE/epoxy composites. While cosmic radiation is deflected by the Earth’s magnetic shield so that very high-energy particles only scarcely reach the ground, this is naturally not the case during space travel. Cosmic rays with high atomic number and energy, also called HZE (High Z and Energy) ions, make up only approximately 1% of the galactic cosmic rays, but due to their high energy and the high charge of these ions, they are as dangerous as the much more frequently occurring protons. Usually, energies up to 10 20 eV/particle can be expected, with the largest particle flux at lower energies and a maximum around 10²–10³ MeV/nucleon. The energy spectrum of all cosmic-ray particles is shown in Figure 1 for higher energies, as measured by different experiments. The so-called primary cosmic rays, which are produced directly through processes in space, mostly consist of protons (~89%), alpha particles (~9%), and other bare nuclei of atoms (~1%), as well as a few solitary electrons (i.e., beta particles, ~1%), that is, positively or negatively charged particles with particle rest masses mostly in the range of 938 MeV/c² (proton) to 3727 MeV/c² (alpha particle) while the secondary cosmic rays, produced by collisions of primary cosmic rays with the atmosphere or with spacecraft or tissue, include many more different particles, such as muons, pions, neutrinos, and neutrons, but also protons and alpha particles, as well as X-rays. Cosmic radiation is nowadays subdivided into high-energy particles stemming from the sun, mostly protons, which are especially emitted in solar eruptions, and high-energy particles stemming from the solar system or from outside of it.
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