Inter-Comparison of Ionizing Doses from Space Shielding Analyses using MCNP, Geant4, FASTRAD, and NOVICE

Several commonly-used space radiation particle transport tools, MCNP, Geant4, FASTRAD, and NOVICE are compared to check consistency of total ionizing dose (TID) estimates for hardware in a harsh-electron Jovian mission environment. Simple geometries with aluminum, tantalum, and a combination of both materials were used to represent typical and high density shields. The forward Monte Carlo (FMC) analyses from MCNP and Geant4 were in a good agreement within run uncertainty. Compared to FMC results, the reverse Monte Carlo (RMC) analysis results from NOVICE and FASTRAD differed by ±20% ~ ±50%, depending on the simple geometrys’ material. The doses from FASTRAD’s ray-tracing methods differed from NOVICE RMC doses by +60% / 10%. TID analyses of complex as-designed geometries from selected flight instruments and electronics boxes were also compared using the NOVICE and FASTRAD tools. The TID results from these complex geometries with aluminum equivalent thickness ranging from 0.1 mil to 3000 mil (3 inches) differed by as much as +200% / 50% between FASTRAD (ray-tracing and RMC) and NOVICE analyses. We conclude that while MCNP and Geant4 FMC analysis results have extensive experimental validation and therefore provide the most accurate TID estimates, RMC analyses are faster to implement and suitable as conservative tools for missions with a sufficient mass margin. We also conclude that ray-tracing analyses can be suitable during the development phase of shield design optimization for its fast runtime capability.