Your Exposure to Radiation

            We are exposed to radiation every day. Most radiation is from natural sources; some is from man-made sources. Naturally occurring sources include cosmic rays from outer space, the sun, the earth’s crust, air, food, and substances in our own bodies. Our exposure to naturally radioactive elements in the earth’s crust may be increased by certain activities such as the mining of minerals, the use of stone and bricks as building materials, and the use of fuels such as coal, geothermal steam, natural gas, and uranium. Man-made sources include fallout from nuclear weapons testing, X-ray machines, and spent fuel from nuclear reactors. Some radioactive materials are used in medical diagnosis and therapy. Others are used in consumer products such as smoke detectors, luminous-dial (LCD) watches, and cardiac pacemakers.

            One measure of radiation is the rad (radiation absorbed dose). A rad is a measure of the energy deposited in a material by ionizing radiation. Since we are often concerned with the protection of people, we frequently use a measurement called rem (roentgen equivalent man). A rem is a measurement of the biological damage caused by radiation. Since we frequently arre exposed to small amounts of radiation, radiation is measured in millirems (mrem), that is, one thousandth of a rem.

            The average dose received by a person living in North America is about 360 mrem annually, or about 1 mrem each day. The exposure varies for each individual depending on where the person lives and what the person does. Living at high elevations results in greater exposure from cosmic radiation than living at sea level.

            Rocks and soil in different regions contain more radioactive elements than those in other regions. Construction of buildings can increase exposure to radiation. For example, the radiation level in parts of New York’s Grand Central Station is equal to 525 mrem per year because of the uranium in the granite rock used in the building.

            The National Council on Radiation Protection and Measurements has set exposure limits. The Council has defined the maximum permissible dose as the highest dose of ionizing radiation that, based on present knowledge, is not expected to cause appreciable bodily harm to a person at any time during his or her lifetime. The Council recommends that the total radiation received by members of the general public from all radiation sources be no more than 500 mrem per year.

            The average dose rate recommended is 170 mrem per year. This does not include radiation exposure necessary for medical purposes. The maximum permissible exposure allowed for someone working with radiation is 5000 mrem per year. Workers at nuclear plants who are pregnant and inform their employer are limited to 500 mrem exposure during the whole pregnancy. Crews of commercial airliners may receive more than 500 mrem from cosmic rays and the sun each year. Exposure is greatest on high altitude flights nearest the poles. Astronauts receive an extra 1000 mrem from each flight.

            All facilities licensed by the Council must reduce employee exposure to radiation to a level that is “as low as reasonable possible.”

Jobs that expose workers to additional radiation each year include:

Average annual radiation dose

Questions:

1. Does most radiation come from natural or human-made sources?

2. What is the average dose of radiation received by a person in North America?

3. According to the National Council on Radiation Protection and Measurements, what is the maximum amount of radiation that you should be exposed to in one year?

4. Estimate your own exposure to radiation by filling in the chart provided. All values are given in mrem/year.

5. According to the chart you completed, did most of your radiation come from natural or human-made sources?

6. List the human-made sources you were exposed to last year.

7. a) How does the amount of radiation you received last year compare to the average dose for North America?

b) How does it compare to the maximum limit recommended by the Council?

8. a) Would a high altitude pilot receive more or less radiation than you received? Explain.

b) Air travelers flying over the North Pole receive 1.4 mrem of radiation per hour. Air travelers flying at 40,000 feet over the equator receive only 0.4 mrem per hour. If you were an airline pilot assigned to the North Pole route, would you be concerned about your radiation exposure? Explain.

c) A female pilot assigned to the North Pole route has just informed you that she is pregnant. It is your job to schedule flights. Will you make any changes in the route assigned to the female pilot? Explain.

9. Does an astronaut receive more or less than the dose limit set by the Council?

10. Based on the information in the textbook Unit II Section 7.1 p. 199, how does the risk of radiation you received compare to the health risks of other daily activities?

Cosmic radiation at sea level - 27

What is the elevation where you live?

Add the number below that corresponds to your elevation in feet;

            1000 feet - 2 mrem     4000 feet - 15 mrem   7000 feet - 40 mrem

            2000 feet - 5 mrem     5000 feet - 21 mrem   8000 feet - 53 mrem

            3000 feet - 9 mrem     6000 feet - 29 mrem   9000 feet - 70 mrem

If your home is within 8 km of a nuclear or coal fired power plant add 0.1 mrem.

If the distance is less than 8 km add zero.

Add the number that identifies the major building material in your home.

            Stone - 100     Brick - 75                               Concrete - 50

            Wood - 35       Aluminum Siding - 35

Add the number beside the region where you live:

            Pacific Coast - 30       Atlantic Coast - 25

            Central - 50                 Gulf Coast - 25

            Southwest - 50            Canadian Shield - 103

What You Eat and Drink

Food and Water - 40

Radon in Air - 200

Nuclear Weapons Fallout - 1

What You Do

Watching television one hour per day - 36.5 mrem

Cooking with natural gas - 15 mrem

Installed smoke detectors - 0.007 for each detector

Being around other people - 0.1 mrem

Flying coast to coast - 4 mrem per round trip

Passing through airport metal detector - 0.001 mrem

Smoking one pack of cigarettes per day - 5000 mrem

Wearing a heart pacemaker - 5000 mrem

Your Medical Exposure

dental x-ray - 10 mrem                       arm x-ray - 20 mrem

chest x-ray - 10 mrem                         leg x-ray - 20 mrem

abdominal x-ray - 500 mrem              radio dye exam - 300 mrem

mammogram - 30 mrem

Your annual Radiation Exposure:         mrem/year