The emission of energy in a stream of particles or waves is radioactivity. While radioactivity can be useful in science and medicine, exposure to high doses of it is dangerous.

Archaeologists can learn the age of certain fossils by measuring their radioactivity — or more specifically, the amount of radioactive carbon they contain. Radioactivity is what creates nuclear power, and doctors also use it in radiation therapy, to kill cancer cells. Too much radioactivity is bad for our bodies, though, since it can damage our DNA. The word comes from radioactivité, which was coined by Marie and Pierre Curie in 1898.

Definitions of radioactivity
  1. noun
    the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
    synonyms: radiation
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    corpuscular radiation, particulate radiation
    a stream of atomic or subatomic particles that may be charged positively (e.g. alpha particles) or negatively (e.g. beta particles) or not at all (e.g. neutrons)
    alpha radiation, alpha ray
    the radiation of alpha particles during radioactive decay
    beta radiation, beta ray, electron radiation
    radiation of beta particles during radioactive decay
    neutron radiation
    radiation of neutrons (as by a neutron bomb)
    type of:
    the release of electrons from parent atoms
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