The Simple English Wikipedia has an article on: Radioactivity Word parts radioactive + -ity Pronunciation IPA (key): /ˌreɪdɪəʊakˈtɪvɪti/ Audio (UK)(file) Noun Singular radioactivity Plural radioactivities Radioactivity is the energy released from an unstable atom.Wikiwand - on Seamless Wikipedia browsing. On steroids.Remove ads