Meaning of RADIOACTIVITY in English

RADIOACTIVITY

ra ‧ di ‧ o ‧ ac ‧ tiv ‧ i ‧ ty /ˌreɪdiəʊækˈtɪvəti, ˌreɪdiəʊækˈtɪvɪti $ -dioʊ-/ BrE AmE noun [uncountable]

the sending out of ↑ radiation (=a form of energy) when the ↑ nucleus (=central part) of an atom has broken apart:

the discovery of radioactivity

high levels of radioactivity

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.