Hydrogen- and Methane-Loaded Shielding Materials for Mitigation of Galactic Cosmic Rays and Solar Particle Events

One of the challenges of human spaceflight in deep space is the harsh radiation environment. The current best practices for mitigating radiation are via design and multifunctional materials. There have been many studies over the years showing low-Z materials as the best radiation mitigators for spaceflight. In addition, there have recently been several studies investigating hydrogen-loading of materials for fuel cells. If it is possible to load a material with additional low-Z materials — such as hydrogen — it may be possible to increase the radiation mitigating potential of these materials. Thus, our work is focused on metal hydrides (MHs), metal organic frameworks (MOFs), and nanoporous carbon composites (CNTs) that can be loaded with hydrogen or methane for radiation mitigation. Our previous simulation work focused on hydrogen-loading only, and investigated the capability of these materials during a particularly hard solar particle event (SPE) in October 1989. In these simulations, we found 50% of the investigated carbon composites outperformed high-density polyethylene (HDPE) — the current standard for passive radiation shielding. We also found 10% of the investigated MOFs outperformed HDPE. Therefore, we wanted to continue our simulation study of these materials to determine whether they may also show improvement over HDPE in a galactic cosmic ray (GCR) environment. Furthermore, there are concerns with using hydrogen as a loading material — a result of its flammability and instability in thermal extremes. Thus, we are also considering methane-loading of the MOFs and CNTs. The details of this work will be discussed in the paper. Overall, the results showed several MOFs, CNTs, and MHs that performed very well when compared with our typical spacecraft material of aluminum and our standard shielding material of HDPE. This study also showed there is little difference in the dose between hydrogen-loaded and methane-loaded materials of the same base chemistry.