Low-energy electron projectiles in water: Linear vs non-linear energy loss

Low-energy electrons as secondary projectiles are behind a significant part of the radiation damage affecting living matter. Research in the optimisation of ion radiotherapy and treatment of radiation poisoning in nuclear-energy environments or outer space make extensive use of Monte Carlo-based cascade simulations (see e.g. [1]) using scattering cross sections and stopping power as input. The ones for electron stopping in liquid water are key input for those simulations. They are customarily obtained from linear-response and phenomenology. Here we present first principles results for the quantum friction for low-energy electron projectiles in water using time-dependent density-functional calculations, both in linear response (frequency domain) and beyond linear, the latter based on explicit real-time simulations. The comparison reveals important deviations, non-linear vs linear, around the Bragg peak, which might be significant for modelling.

[1] K. P. Chatzipapas, P. Papadimitroulas, D. Emfietzoglou, S. A, Kalospyros, M. Hada, A. G. Georgakilas, and G. C. Kagadis, Cancers 12(4), 799 (2020).