Simulation of the Heavy Ion Contribution to the Radiation Environment onboard the International Space Station

Abstract: The health risks from exposure to the space radiation environment makes it important to have reliable simulation models for the radiation doses inside spacecrafts. Simulations of the heavy ion parts, especially iron, of the Galactic Cosmic Ray (GCR) radiation has been carried out using the simulation software Geant4 with geometry models from the DESIRE project. The total dose rate from iron ions is found to be 1.57 Gy=d and dose equivalent is found to be 17 Sv=d. This means that iron contributes between 5% and 10% to the total dose equivalent from the GCR radiation, substantially higher than its relative abundance of 0.03 percent. 67% of the dose rate from iron comes from particles with energies in the range 1 000 - 10 000 MeV/nucleon, and 26% comes from particles in the 10 000 - 50 000 MeV/nucleon range. The great majority of the dose is deposited by iron ions, opposed to secondary particles. This result was not expected. Calculated dose rates are found not to be significantly dependent of the ISS altitude.