Once astronauts venture beyond Earth’s protective atmosphere, they are exposed to the high-energy charged particles of galactic cosmic rays (GCR) and solar particle events (SPE), and secondary protons and neutrons. GCR are composed of ions, the great majority of which are protons (≈87%) and helium nuclei (≈12%). The heavy ions of atomic number greater than 2 comprise only a small fraction of the charged particles in the GCR, but they contribute significantly to the radiation dose and dose equivalent over time. Because of their ionization patterns in biomolecules, cells and tissues are distinct from terrestrial radiation, the resulting biological effects are poorly understood, and the health risks of these radiations are subject to large uncertainties.
The code RITRACKS has been developed at NASA Johnson to simulate the effects of ionizing radiation at the microscopic scale, and to understand the effects of space radiation at the biological level. The fundamental part of this code is the stochastic simulation of radiation track structure of heavy ions, an important component of space radiations. The code can calculate many relevant quantities such as the radial dose, voxel dose, and may also be used to calculate the dose in spherical and cylindrical targets of various sizes.
Recently, DNA structure and damage simulations were incorporated at the molecular scale in RITRACKS. The direct effect of radiation is simulated by introducing a slight modification of the existing particle transport algorithms using the Binary-Encounter-Bethe model of ionization cross-sections for each molecular orbital of DNA. The simulation of radiation chemistry is done by a step-by-step diffusion reaction program based on the Greens functions of the diffusion equation. This approach is also used to simulate the indirect effect of ionizing radiation on DNA. The software includes a graphical user interface (GUI) and a 3D OpenGL visualization interface. The calculations are executed simultaneously (in parallel) on multiple CPUs (central processing units).
RITRACKS is different from similar existing codes in several ways. It is a standalone application that can be installed on 64-bit machines running on Windows. It is used for microscopic applications, and a visualization interface for the tracks in 3D is included. Minimal knowledge of Monte Carlo track structure simulations is required to use the program.
This work was done by Ianik Plante of Wyle Laboratories for Johnson Space Center. This software is available for use. To request a copy, please visit https://software.nasa.gov/software/MSC-25937-1 .