Living things have evolved in an environment which has significant levels of ionising radiation. Furthermore many of us owe our lives and health to such radiation. Medical and dental X-rays discern hidden problems. Other radiation is used to diagnose ailments and some people are treated with radiation to cure disease. 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. 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.