A GPU‐based Monte Carlo model for water radiolysis under ultra‐high dose rate irradiation: Development and validation with MPEXS2.1‐DNA

We developed a GPU-based computational framework for water radiolysis simulations under UHDR conditions using MPEXS2.1-DNA. Our step-by-step approach enabled spatially precise tracking of intertrack reactions among radiolysis species originating from different proton tracks, a capability not achievable with conventional simplified methods. Additionally, we demonstrated that large-scale statistical analysis is computationally feasible under UHDR conditions through GPU acceleration. Our results successfully reproduced the experimental trends for the G values of hydroxyl radicals and hydrated electrons. Oxygen depletion rates also showed good agreement with experimental measurements. However, the discrepancy between simulated and measured G values of hydrogen peroxide indicates the need to incorporate additional competitive reactions, potentially including third-order mechanisms, for future UHDR modeling studies.