Figure 1 illustrates that the largest contribution of radiation exposure to the public is from natural sources of radiation, namely radon, and cosmic radiation.

Source: National Council on Radiation Protection and Measurements (NCRP), 1987, "Ionizing Radiation Exposures of the Population of the United States", Report No. 93, Washington, DC: National Council on Radiation Protection and Measurements.

* The NCRP backround information for their chart included under "Other" exposures; Occupational, Fallout, Nuclear Fuel Cycle, and Miscellaneous with a total exposure from these sources of 0.8%.   This resulted in a chart total of 100.8%.  We have rounded up 0.8% "Other" exposures to 1%, and reduced the radon estimated exposure by 1% so that the total will not exceed 100%.  The reader should be reminded that these percentages are estimates and, as noted in the NCRP report, "...subject to various uncertainties..."