What are the sources of radiation?
Ionising radiation and radioactive substances are natural and permanent features of the environment. These sources, called natural background radiation, consist principally of cosmic rays entering the earth s atmosphere; terrestrial gamma rays due largely to uranium and thorium, including their decay products, found in various low concentrations throughout the earth s crust; potassium 40, a radioisotope which is mixed in small concentrations in nature with stable potassium; and radon decay products. Through natural background radiation, people are exposed to external radiation and internal radiation by inhalation and ingestion of radioactive substances existing in the natural environment.
Artificial radioactivity resulting from nuclear weapons programmes, principally atmospheric testing, is also spread throughout the world and exposes people to external radiation and internal radiation through inhalation and ingestion. However, the average dose to individuals in the world population from military activities is very small compared to that resulting from natural background radiation, and is declining due mainly to the atmospheric test ban treaty of 1963, but also to the general reduction of nuclear weapons programmes. Some countries are now faced with the difficult task of decontamination and stabilisation of military weapons test and production sites.
Additionally, the use of man-made radiation is widespread. These sources of ionising radiation are called practices. The use of nuclear energy and applications of its by-products (i.e., ionising radiation and radioactive substances) continue to increase around the world. In addition to nuclear power production, nuclear techniques are used in industry, agriculture, medicine and many fields of research, benefiting hundreds of millions of people and giving employment to millions of people in the related occupations. For example, medical X-rays and nuclear medicine are vital diagnostic tools, and radiotherapy is commonly part of the treatment of cancer. Large irradiators are used in many countries to sterilise medical products, preserve foodstuffs and reduce wastage, and sterilisation techniques have been used to eradicate disease-carrying insects and pests. Industrial radiography is in routine use to examine welds for defects and help prevent the failure of engineered structures. Radiotracers are used in many fields of research.Figures 1 and 2 show the estimated percentage dose contribution of various sources, both natural and artificial, averaged to individual members of the population in the United Kingdom and the United States, respectively. The percentage contribution of the sources to any specific individual will vary from the average depending on a variety of factors (e.g., increased cosmic radiation for those living at high altitudes, individuals receiving medical radiation diagnosis or treatment). Although there are some differences in the way in which source contributors are categorised in Figures 1 and 2, it should be noted that the average dose from natural sources dominates the dose from all other sources combined, estimated to be 87% and 82% for the United Kingdom and the United States, respectively.