Radiation risk management for human space missions dependson accurate modeling of high-energy heavy ion transport in matter. Theprocess of nuclear fragmentation can play a key role in reducing both thephysical dose and the biological effectiveness of the radiationencountered in deep space. Hydrogenous materials and light elements areexpected to be more effective shields against the deleterious effects ofGalactic Cosmic Rays (GCR) than aluminum, which is used in currentspacecraft hulls. NASA has chosen polyethylene, CH2, as the referencematerial for accelerator-based radiation testing of multi-functioncomposites that are currently being developed. A detailed discussion ofthe shielding properties of polyethylene under a variety of relevantexperimental conditions is presented, along with Monte Carlo simulationsof the experiments and other Monte Carlo calculations in which the entireGCR flux is simulated. The Monte Carlo results are compared to theaccelerator data and we assess the usefulness of 1 GeV/amu 56Fe as aproxy for GCR heavy ions. We conclude that additional accelerator-basedmeasurements with higher beam energies would be useful.

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