radioactivity

noun

1. (uncountable, usually)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. (uncountable, usually)The radiation so emitted; including gamma rays, alpha particles, neutrons, electrons, positrons, etc.