Radiation dose simulation of a water phantom in the cabin of an interplanetary spacecraft

The radiation exposure received by astronauts on deep-space missions must be considered in the design of future spacecraft. Galactic cosmic rays (GCR) include high-energy heavy ions, which can often penetrate the thickest shielding that can be practically launched with a spacecraft. Some of these heavy ions deliver a very high radiation dose per particle, and this highly ionizing radiation is more damaging per unit dose than sparsely ionizing radiation. Nuclear fragmentation is the principal physical mechanism by which the dose delivered by these particles can be reduced. This study reports models of the interactions of heavy ions from galactic cosmic rays in a maimed spacecraft. The models were built and analyzed in the Geant4 toolkit. The total and secondary particle dose depth distributions in a water phantom were estimated using Monte-Carlo simulation. Heavy ions of 400 A MeV C-12, 600 A MeV O-16, 1000 A MeV Si-28, 1000 A MeV Fe-56 were modeled as traversing a simple spacecraft wall to reach a water phantom. The simulations predict the Bragg curves of different forms of radiation in the water phantom. This curve is used to calculate the contributions to the total radiation dose from charged secondary fragments, primary-beam nuclei, and other particles produced from nuclear fragmentation reactions.