https://doi.org/10.1351/goldbook.14073
Chemical change or physical process occurring in one entity (e.g., biological molecules, cells, and living organisms) as a result of initial absorption of high-energy radiation by the medium in the presence of another entity called the radiation sensitiser.
Note: High-energy radiation is absorbed usually nonspecifically in the medium (e.g., solvent) and all chemical reactions arise from the products of this primary energy absorption.