Ionizing radiation is the energy or particles (protons, electrons or neutrons) produced by unstable atoms of radioactive materials. It is present in the environment, as a result of both naturally occurring radioactive minerals and cosmic radiation arriving from outer space. Ionizing radiation is also produced by certain human activities, such as medicine and industry, and may result from accidents in nuclear facilities and nuclear bomb explosions.
When absorbed by the body, radiation produces toxic free radicals. Exposure to high levels of radiation can cause substantial damage to human body tissues, and may lead to death. Prolonged exposure to lower levels is also associated with increased risk of ill-health.