Speaker
Description
Neutron radiation—encountered in healthcare, nuclear reactors, and the space environment—is extremely damaging to human health. On the lunar surface, galactic cosmic rays interact with the lunar regolith to produce albedo neutrons, which have energies ranging from sub-eV to tens of MeV, making it of critical importance to shield these albedo neutrons for manned space exploration missions. Using polymer-based materials mixed with hexagonal boron nitride, we consider the physical processes of moderation and absorption to address a basic question: To protect human health, what is the optimal distribution of thermalization and capture elements within a shielding material? Using Geant4, a Monte Carlo code, we simulate over ~20,000 configurations. We find the answer to our original question is nuanced – generally, alternating layers of capture and moderation materials improve radiation protection compared to blended composites but this is not the case for all neutron energies and composite thicknesses. By optimizing the internal structure, we improve the shielding effectiveness up to a factor of 72 relative to aluminum. This is a significant improvement that could dramatically reduce the occupational radiation dose for workers in high-risk environments. Through our new NASA SSERVI program (called CLEVER), we plan to expand our Geant4 capabilities to simulate the charge transport in lunar regolith upon radiation exposure. Our goal is to track the defects, impurities, vacancies, dislocations, and other forms of inhomogeneities on the surfaces and in the crystalline structure of lunar regolith for general particle source.
