Radiation Protection

Radiation Sources and Doses

Sources of radiationHelpradiationEnergy given off as either particles or rays. are all around us all the time. Some are natural and some are man-made. The amount of radiation absorbed by a person is measured in dose. A dose is the amount of radiation energy absorbed by the body. See Radiation Basics for information about dose.

All of us are exposed to radiation every day, from natural sources such as minerals in the ground, and man-made sources such as medical x-rays. According to the National Council on Radiation Protection and Measurements (NCRP), the average annual radiation dose per person in the U.S. is 620 milliremHelpmilliremThe millirem is the U.S. unit used to measure effective dose. One millirem equals 0.001 rem. The international unit is milliSievert (mSv). (6.2 millisieverts). The pie chart below shows the sources of this average dose.
NCRP Report No. 160, Sources of Radiation Exposure,Pie chart of annual Sources of Radiation Exposure, 37 percent comes from radon and thoron, 5 percent comes from space, 5 percent comes from internal, 3 percent comes from terrestrial, 24 percent comes from computed tomography, 12 percent from nuclear medicine, 7 percent from interventional fluoroscopy, 5 percent from conventional radiography, 2 percent from consumer products, O,1 percent from occupational sources, Less than 0,1 percent from industrial sources.Figure reprinted with permission of the National Council on Radiation Protection and MeasurementsExit

Most of our average annual dose comes from natural background radiationHelpbackground radiationRadiation that is always in the environment. The majority of background radiation occurs naturally and a small fraction comes from man-made elements. sources:

  • The radioactive gases radon and thoron, which are created when other naturally occurring elements undergo radioactive decay.
  • Space (cosmic radiation).
  • Naturally occurring radioactive minerals:
    • Internal (in your body).
    • Terrestrial (in the ground).

Another 48 percent of the average American’s dose comes from medical procedures. This total does not include the dose from radiation therapy used in the treatment of cancer, which is typically many times larger.

Use the Radiation Dose Calculator to estimate your yearly dose from sources of ionizing radiation.

The following diagram compares radiation doses from common radiation sources, both natural and man-made.

Relative Doses from Radiation Sources, Whole body CT is 1000 millirems, upper gastrointestinal fluoroscopy 600 millirems, radon in average U S home 228 millirems, a head C T 200 millirems, cosmic radiation in Denver 80 millirems per year, a mammogram 42 millirems, cosmic radiation at sea level 30 millirem, radiation in the body 20 millirems, terrestrial radioactivity 21 millirems, chest x-ray 10 millirems, living near nuclear power plant less than 1 millirem.


National Council on Radiation Protection & Measurements (NCRP), Report No. 160 Exit

International Commission on Radiological Protection, Publication 103 Exit