/ ˌreɪdiəʊˈæktɪv; NAmE -oʊˈæk-/ adjective
sending out harmful radiation caused when the nuclei (= central parts) of atoms are broken up
► radio·activ·ity / ˌreɪdiəʊækˈtɪvəti; NAmE -oʊæk-/ noun [ U ]:
the study of radioactivity
a rise in the level of radioactivity