Lesson 11d - Understanding the Basics of Radiation
Natural Sources of Radiation (cont.)
Internal Radiation

Humans have carried trace amounts of radioactive materials in their bodies ever since there were humans, because people must eat and drink. Most people don't realize that the food and water necessary to sustain life contain very small amounts of natural radioactive materials. Digesting naturally occurring radioactive materials, such as Na-24, C-14, Ar-41, and K-40, leaves extremely small deposits of these materials in the human body, and these small deposits emit radiation. All the radioactive materials mentioned above are sources, but potassium is responsible for most of the internal radiation exposure to humans, which averages between 39 and 40 mrem a year.
The chart below identifies a few typical foods that contain potassium and therefore contribute to internal radiation. The number of milligrams listed for the amount of potassium in each food should not be confused with the amount of radiation that food will produce. Potassium radiation measurements are calculated on a different scale than the millirem unit, and the chart is offered only as a way of comparing internal sources to other types of sources.
Potassium Content and Potassium-40 Activity
in Some Selected Foods
Food Portion Potassium (mg) K-40 (mg)
Hot Dogs 2 regular 200 2.4
Hamburger 4 ounces 960 11.52
Chicken, Fried 1/4 chicken 240 2.88
French Fries 3.5 ounces 650 7.8
Broccoli 1 stalk 270 3.24
Corn 1 ear 200 2.4
Banana 1 small 240 2.88
Orange 1 medium 300 3.6
2% Milk 1 cup 380 4.56
Ice Cream 4 ounces 50 0.06
Pepsi Cola 12 ounces 13 0.156
Coca Cola 12 ounces 4 0.048
Bran Flakes 1 ounce 140 1.68
Corn Flakes 1 ounce 14 0.168
Whole Wheat Bread 1 slice/1 ounce 70 0.84
White Bread 1 slice/1ounce 30 0.36
Sunflower Seeds 3.5 ounces 920 11.04
Peanut Butter 1 ounce 110 0.396
Egg 1 large 65 0.78
Note: 0.012 percent of all Potassium occurs as the Potassium-40 isotope.
Source: Potassium concentrations from U.S. Dietary Goals, U. S. Department of Agriculture and Natow, A.B. and J Heslin, Nutrition for the Prime of Your Life, New York, McGraw, 1984.

Click here to access a worksheet using the above chart.
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