Radiation chemistry is a subdivision of nuclear chemistry which is the study of the chemical effects of radiation on matter; this is very different from radiochemistry as no radioactivity needs to be present in the material which is being chemically changed by the radiation
An example is the conversion of water into hydrogen gas and hydrogen peroxide
P Wardman. Br J Radiol. 2009 Feb. The importance of radiation chemistry to radiation and free radical biology (The 2008 Silvanus Thompson Memorial Lecture) (PMID: 19168690)