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..."