radioactivity C1 Topic:Science & Research Also spelled radio-activity US /ˌreɪdɪəʊakˈtɪvɪti/ See IPA manual Freq #22820 Meanings 1 noun Spontaneous emission of ionizing radiation as a consequence of a nuclear reaction, or directly from the breakdown of an unstable nucleus. Today, no one would intentionally smear radioactive materials on their face, but in 1933, the dangers of radioactivity were not yet fully understood. 2 noun the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay 3 noun The radiation so emitted; including gamma rays, alpha particles, neutrons, electrons, positrons, etc. Thesaurus Synonyms 2 noun · the spontaneous emission of... radiation Word family Derived forms nonradioactivity Related forms activitybecquerelcuriehalf-liferadiationradio- Etymology From radioactive + -ity or radio- + activity. Topics Science & Research External links Cambridge Dictionary Wiktionary Google Images # radioactivity **Type:** Word **Level:** C1 **Part of speech:** noun **IPA (US):** /ˌreɪdɪəʊakˈtɪvɪti/ **Frequency rank:** 22820 ## Meanings 1. Spontaneous emission of ionizing radiation as a consequence of a nuclear reaction, or directly from the breakdown of an unstable nucleus. 2. the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay 3. The radiation so emitted; including gamma rays, alpha particles, neutrons, electrons, positrons, etc. ## Examples - Today, no one would intentionally smear radioactive materials on their face, but in 1933, the dangers of radioactivity were not yet fully understood. ## Derived Forms - nonradioactivity ## Related Forms - activity - becquerel - curie - half-life - radiation - radio- ## Etymology From radioactive + -ity or radio- + activity. ## Topics - Science & Research markdown