We all benefit from a multitude of products and services made possible by the careful use of radioactive materials. Background radiation is that which is naturally and inevitably present in our environment. Levels of this can vary greatly. People living in granite areas or on mineralised sands receive more terrestrial radiation than others, while people living or working at high altitudes receive more cosmic radiation. A lot of our natural exposure is due to radon, a gas which seeps from the earth's crust and is present in the air we breathe.
Radiation comes from atoms, the basic building blocks of matter.
These atoms are said to be 'unstable' or 'radioactive'. An unstable atom has excess internal energy, with the result that the nucleus can undergo a spontaneous change to a more stable form. This is called 'radioactive decay'. Some elements, eg uranium, have no stable isotopes. When an atom of a radioisotope decays, it gives off some of its excess energy as radiation in the form of gamma rays or fast-moving particles.