Effectiveness of shielding materials for dose reduction

The design of future spacecraft such as the Crew Exploration Vehicle must take into account the radiation shielding properties of both the structural components as well as dedicated shielding materials. Since the vast majority of solar energetic particles (SEP) are stopped by modest depths of shielding, the far greater challenge is posed by the need to shield crew from the galactic cosmic rays (GCR), which include highly-charged and highly-energetic particles. Hydrogenous materials and low-mass elements have been shown to be more effective shields against the deleterious effects of GCR-like irradiations than the aluminum currently used in spacecraft hull design. Polyethylene, CH₂, has therefore been chosen by NASA as the reference material for comparison of multifunction composites currently being developed. A wide variety of targets, both elemental and composite, were placed in the particle beams, and the spectra of particles emerging from the targets were measured using a stack of silicon detectors. Results are presented in terms of dose reduction per g cm^-2 of target material, and compared to an equal mass of CH₂