radioactivityPronunciation: /ˌreɪdɪəʊakˈtɪvɪti/Translate radioactivity | into German | into Italian | into Spanish Definition of radioactivity noun [mass noun] the emission of ionizing radiation or particles caused by the spontaneous disintegration of atomic nuclei. radioactive substances, or the radiation emitted by these: an escape of radioactivityradioactivity in other Oxford dictionaries Definition of radioactivity in the US English dictionary
