Answer to Question #36450 in Atomic and Nuclear Physics for kaira
causes of background radiation
Background radiation comes from both natural and artificial sources, although the majority (97%) of human exposure comes from natural sources. These natural sources include cosmic rays from space that hit the Earth, radon gas that comes from under ground, and naturally occurring radioactive elements such as radium, thorium, and uranium that leach into water and food from the earth.
About 3% of background radiation comes from man-made sources, such as global contamination from weapons testing, power generation, medical uses, and burning fossil fuels. As for its significance, that is debatable. The average dose of radiation exposure is 3.6 millisievert per year.
As a comparison, a typical X-ray gives you a dose of about 0.02 to 0.2 millisievert. Many biologists actually consider small amounts of radiation to be healthy for biological organisms and populations in general.