The radiolysis of water molecules by ionizing radiation leads to the production of various reactive species, which play a critical role in the indirect killing of cancer cells. In radiotherapy (RT) techniques involving nuclear reactions, both radiolysis-induced radical generation and nuclear reaction processes are present within the irradiated environment. However, the interaction between these two mechanisms remains poorly understood, limiting further optimization of RT. In this work, the effect of the ${}^{15}\mathrm{N}(p,\alpha ){}^{12}\mathrm{C}$ reaction on the kinetic energy release of water fragmentation and on the kinetic energy (KE) of the generated radicals is investigated using a point-charge model. It is found that the charge state $q$ and flight velocity $v$ of the nuclear reaction products are the primary influencing factors. Additionally, lighter and more distant radicals produced by the nuclear reaction are observed to obtain higher KEs. These radicals may influence the local spatial distribution of reactive species and their interaction with nearby biomolecules. A feasibility analysis indicates that such effects can be experimentally measured using a cold target recoil ion momentum spectroscopy. The primary motivation of this study is to provide atomic- and molecular-level insights into how nuclear reactions influence water fragmentation in RT, laying a foundation for future experimental and biological investigations.

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• Atomic & molecular collisions
• Medical physics & public health
• Radiation therapy