Radiation Shielding Simulation of High Energy Neutrons for Small Instrument Packages

Enabling radiation shielding technology is imperative for deep space exploration of spacecraft and crewed missions to the moon and Mars. Radiation from the sun's gamma rays and from high energy neutrons due to cosmic rays prove to be some of the toughest particles to shield electronics from. Typically shielding is implemented up to the gamma limit and then radiation hardened electronics are used to protect against higher-energy gamma rays and neutrons. Neutrons pose a problem for electronics due to their high energy and mass having a significant impact on silicon substrates. However, well-designed shielding can be used as protection from high energy neutrons as well, through the use of moderator and absorber materials. It has been shown that when using them in combination, they have the capacity to decrease neutron energy and absorb them, respectively. The moderator + absorber layer concept has been utilized for large-scale, ground-based systems such as nuclear facilities. We look at incorporating the same concept with a small form factor for instrument packages bound for deep interplanetary space. Preliminary results simulated in a software package known as SWORD7 will be shown for a novel radiation shielding concept that attenuates high-energy neutrons. Simulation runs of a 15 day equivalent fluence were performed and analyzed for a 1U CubeSat module (10 cm³) using various materials for a moderator layer and absorber layer, and compared them with minimal shielding to analyze shielding success. The combination of polyethylene as a moderator layer and boron carbide as an absorber layer were proven to be the best solution of all combinations including a stainless steel only case.