Radiation is a part of nature and each of us is exposed to radiation. Sources of radiation can be divided into two types: natural background radiation and man-made radiation.
Natural Radiation Sources
Natural radiation accounts up to 85% of the annual human radiation dose and includes cosmic radiation, terrestrial radiation and internal radiation.
Cosmic radiation is coming from the sun and from outer space. The doses due to natural sources of radiation vary depending on location and to the effects of the earth’s magnetic field.
Terrestrial radiation is associated with the composition of the earth's crust. Important radioactive elements include uranium-238 and thorium-232 and their radioactive decay products. For example, radon gas is produced by the decay of uranium, has no smell or color and can be accumulated in buildings, thus it can be very harmful for people. On average, it is the largest source of natural radiation exposure.
People can also face terrestrial radiation in the oil and gas industries, where it is known as Naturally Occurring Radioactive Material (NORM). In the process of mining radon or radium can be accumulated in pipes or contaminate the surfaces and thus be very harmful for people.
The amount of terrestrial radiation varies in different parts of the world due to different concentrations of uranium and thorium in soil.
Internal radiation implies that radioactive substances exist in the air the man is breezing, in food or water and penetrate the human body through inhalation or ingestion. The most important internal radioactive element is naturally occurring potassium-40.
Man-made radiation sources
Radiation from man-made sources accounts up to 20% of the public’s exposure annually.
There are two distinct groups exposed to man-made radiation sources, these are:
- Members of the public
- Occupationally exposed individuals
X-rays and medical procedures, such as diagnostic X-rays, nuclear medicine, and radiation therapy, are the most significant sources of man-made radiation exposure to the public. To a lesser degree, members of the public are exposed to radiation from consumer products, building materials, combustible fuels, airport X-ray systems etc.
Nuclear power, nuclear weapon testing and accidents account only 1% among all man-made sources of exposure.