Radioactivity in Food

Many of the foods we eat contribute to our internal exposure to radiation. These foods are naturally radioactive. They contain elements like potassium (K) and carbon (C) that are essential for good health and cannot be eliminated from our diets.

Potassium-40

Potassium-40 is a radioactive isotope of naturally occurring potassium. Potassium-40 contributes 18 millirem to our average annual internal radiation exposure.

Directions: Use the food chart entitled Potassium Content and Potassium-40 Activity in Some Selected Foods to answer the following questions.

1. List four foods you have eaten this week that contain potassium.

Disintegration is the name given to the physical act of an atomic nucleus breaking into two or more smaller pieces, that is, of undergoing radioactive decay or fission. Radiation is measured in disintegrations (decays) per second. .

2. .If the radioactivity of 1 gram of natural potassium is 30 disintegrations per second (d/sec) and a small banana contains about 0.4 grams of natural potassium, what is the number of disintegrations per second of this banana?

3.The activity of the radioactive potassium-40 in your body is about 60 disintegrations per second per kilogram (d/sec/kg) of body weight.

a. How much do you weigh? (in pounds)

b. If 1 kg = 2.2 lbs., how much do you weigh in kilograms?

c. Given the activity of potassium-40 above, what is the activity of potassium-40 in your body in disintegrations per second (d/sec)?

Carbon-14

The second largest contributor to our annual internal exposure is carbon-14, a naturally occurring radioactive isotope of carbon. It contributes about 1.2 millirem to our average annual internal radiation exposure.

4. Our bodies are about 23 percent carbon by weight. Because it contains some carbon-14, the carbon in your body has an activity of 227 disintegrations per second per kilogram.

a. Based on your weight in kilograms, how much of your body is carbon? Express your answer in kg of carbon.

b. Given the activity of carbon-14 in the carbon of your body, what is the total activity of the carbon in your body?

Carbon, Potassium, and Your Health

5. Should you try to eliminate all potassium or carbon from your diet in an effort to reduce your annual internal exposure to ionizing radiation? Why or why not?

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