radioactivityEnglishOxford Dictionary of Englishradioactivity /ˌreɪdiəʊakˈtɪvɪti / ▸ 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 radioactivity.
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EnglishOxford Dictionary of English