Shielding experiments with high-energy heavy ions for spaceflight applications

Mitigation of radiation exposures received by astronauts on deep-space missions must be considered in the design of future spacecraft. The galactic cosmic rays (GCR) include high-energy heavy ions, many of which have ranges that exceed the depth of shielding that can be launched in realistic scenarios. Some of these ions are highly ionizing (producing a high dose per particle) and for some biological endpoints are more damaging per unit dose than sparsely ionizing radiation. The principal physical mechanism by which the dose and dose equivalent delivered by these particles can be reduced is nuclear fragmentation, the result of inelastic collisions between nuclei in the hull of the spacecraft and/or other materials. These interactions break the incident ions into lighter, less ionizing and less biologically effective particles. We have previously reported the tests of shielding effectiveness using many materials in a 1 GeV nucleon^{−1 56}Fe beam, and also reported results using a single polyethylene (CH₂) target in a variety of beam ions and energies up to 1 GeV nucleon⁻¹. An important, but tentative, conclusion of those studies was that the average behavior of heavy ions in the GCR would be better simulated by heavy beams at energies above 1 GeV nucleon⁻¹. Following up on that work, we report new results using beams of ¹²C, ²⁸Si and ⁵⁶Fe, each at three energies, 3, 5 and 10 GeV nucleon⁻¹, on carbon, polyethylene, aluminium and iron targets.