The part of chemistry which deals with the chemical effects of ionizing radiation, as distinguished from photochemistry associated with visible and ultraviolet electromagnetic radiation.
Sources:
Orange Book, 2nd ed., p. 236 (https://media.iupac.org/publications/analytical_compendium/)
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2523 (https://doi.org/10.1351/pac199466122513)