Health action in crises

FAQs: Japan nuclear concerns

15 March 2011

Ionizing radiation

What is ionizing radiation?

  • When certain atoms disintegrate, either naturally or in man made situations, they release a type of energy called Ionizing radiation (IR). This energy can travel as either electromagnetic waves (gamma or X-rays) or as particles (neutrons, beta or alpha).
  • The atoms that emit radiation are called radionuclides.
  • The time required for the energy released by a radionuclide to decrease by half (i.e., the "half-life") range from tiny fractions of a second to millions of years depending on the type of atoms.