Current Status of Hetc-heds Radiation Transport Code Development

One of the hazards faced by crews of spacecraft in space is exposure to ionizing radiation in the space environment. The main sources of these radiations are the trapped radiation in the Van Allen belts, consisting mainly of protons in the inner belt and electrons in the outer belt, the galactic cosmic ray (GCR) background, composed of all naturallyoccurring elements, and solar energetic particles, produced by events, such as coronal mass ejections and associated phenomena on the Sun. As these radiations pass through spacecraft shielding, their energies and composition are altered by atomic and nuclear interactions with the shielding. Transport of the space radiation fields, as they pass through shielding and body materials, can be mathematically simulated by transport codes utilizing either solutions of the Boltzmann equation or Monte Carlo techniques, obtained by balancing changes in particle fluxes as they traverse a small volume of material with the gains and losses caused by atomic and nuclear collisions. Recently, the Monte Carlo radiation transport code HETC, originally developed at Oak Ridge National Laboratory, has been extended to include heavy ion nuclear interaction models and the associated software modifications needed for heavy ion tracking [1]. The resulting code, called HETC-HEDS (High Energy Transport Code Human Exploration and Development of Space), is capable of carrying out three-dimensional transport of all components, including heavy ions, of the space radiation environment. In this work we present an overview of the current status of code development and present comparisons of predictions from this newly-developed tool with recent laboratory beam measurements of the fluences of secondary particle species produced by the interactions of cosmic ray heavy ion species with thick targets. We also present comparisons of the code predictions with predictions from the PHITS code, recently developed by researchers in Japan.