Radiation is energy traveling in the form of particles or waves in bundles of energy called photons. Some everyday examples are microwaves used to cook food, radio waves for radio and television, light, and x-rays used in medicine.
Radiation is energy that is either ionizing or non-ionizing. Ionizing radiation – invisible waves and particles emitted from radioactive atoms include alpha, beta, x-ray, gamma and neutron radiation. Some atoms (e.g., uranium and thorium) are naturally radioactive, whereas others (e.g., tritium and iodine-131) can be made radioactive in reactors or accelerators.
Radioactivity is a natural and spontaneous process by which the unstable atoms of an element emit or radiate excess energy in the form of particles or waves. These emissions are collectively called ionizing radiations. Depending on how the nucleus loses this excess energy either a lower energy atom of the same form will result, or a completely different nucleus and atom can be formed.
(Average annual radiation dose in the US from natural and manufactured radiation sources)
Background radiation is radiation from our natural environment. It comes primarily from cosmic rays, radioactive material in the earth, naturally occurring radionuclides (such as potassium-40) in food, and radon gas that is in the air we breathe. In the United States, the average background radiation dose is about 300 mrem/year.
Manufactured sources of radiation contribute an additional dose of approximately 60 mrem/year, of which approximately 54 mrem/year is from medical procedures (e.g., x-rays and certain diagnostic tests). Consumer products (e.g., lantern mantles and smoke detectors) contribute roughly 6 mrem/year.
(Other sources of Radiation)
Fallout radiation (still present in our environment from the era of above-ground nuclear testing) contributes less than 1 mrem/year. Figure 2 shows typical annual radiation doses in the United States.