radioactivity
n.the process by which some materials give off energy and invisible rays. This happens because the atoms in these materials are unstable and change over time.
n.the spontaneous emission of ionizing radiation from the nucleus of an atom, typically as a result of radioactive decay.
“The scientist measured the radioactivity of the sample.”
“The nuclear power plant is designed to safely manage the radioactivity produced by the fission of uranium atoms.”
“While natural radioactivity is a constant background presence on Earth, the sudden increase in levels at the site raised significant concerns among the environmental monitoring team.”
“Each shipment should be checked for radioactivity when entering ports or crossing borders.”
“Over that period, the detector recorded around 100 antineutrino candidate events linked to residual radioactivity in the reactor cores and nearby spent-fuel cooling pools.”
From radioactive + -ity or radio- + activity.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.