Biological risk of GCR determined using PHITS and FLUKA simulation

Galactic Cosmic Rays (GCR) pose a substantial risk to humans in space.
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Uncertainties in risk estimates, caused by the interaction of GCR in human tissue, stem primarily from uncertainties in quality factors. The generally accepted methods for determining Quality Factor don't account for differences in particle tracks of different ions with equal Linear Energy Transfer (LET). The LET can also be equal for different particle species with different velocities but radiobiological studies often indicate differing levels of damaging ability. Ionization density of particle tracks for different ions of equal LET decreases with increasing atomic number and velocity. In this case, the heavier and higher velocity ions produce a wider delta ray penumbra and, therefore, a lower ionization density for the same dose to a target. Variations in the particle trajectories of different ions cause a change in energy deposition and the resulting target effects on the cellular level. This paper presents findings that account for variations in particle traversals of different ions and compares the ionization densities of their tracks. Transport modeling, using the Particle and Heavy Ion Transport Code System (PHITS) and FLUKA tool kits provide this function and is compared with well-accepted theoretical models developed by A. Chatterjee (1976) and J.J. Butts and R. Katz (1967).