CHAPTER 10 13 SECTION Nuclear Changes Nuclear Radiation Today KEY IDEAS As you read this section, keep these questions in mind: Where are some common sources of radiation? What are some beneficial uses of nuclear radiation? What factors determine the risks of nuclear radiation? How is the energy produced by nuclear fission used? Is All Radiation Harmful? You may be surprised to learn that you are exposed to some form of nuclear radiation every day. Some forms of nuclear radiation are beneficial. Others may be harmful. As you read this section, you will learn about some benefits and risks of nuclear radiation. Where Is Radiation? Nuclear radiation is all around you. Every day, we are exposed to radiation from natural sources, such as the sun, soil, and rocks. Nuclear radiation that comes from natural sources is known as background radiation. About 80% of all radiation we are exposed to comes from natural sources. The living tissues of most organisms are adapted to survive the low levels of natural nuclear radiation. About 20% of our exposure to nuclear radiation comes from human-made sources. These sources include smoke detectors and X rays. READING TOOLBOX Outline As you read this section, make an outline to summarize the main points. Use the headers throughout the section to help you organize your outline. 1. Define What is background radiation? 2. Identify Give two sources of background radiation that you can see in this picture. Interactive Reader 221 Nuclear Changes
3. Define What is a rem? MEASURING RADIATION Levels of radiation absorbed by the human body are measured in rems or millirems (1 rem = 1,000 millirems). An X ray at the dentist s office exposes a patient to about 1 millirem of radiation. In the United States, many people work in jobs that involve nuclear radiation. These include nuclear engineers, medical technicians, and some scientists. A safe limit for such workers has been set at 5,000 millirems per year. This level does not include exposure to natural background radiation. Research In a small group, choose one of the cities listed in the table. Compare the level of radiation exposure for that city with others in the table. Is the level higher or lower? Research the geography and climate of this city. What factors may cause this city to have a higher or lower level of radiation exposure than other cities? Present your findings and ideas to the class. EXPOSURE BY LOCATION People in the United States receive different amounts of natural radiation. People who live at higher elevations are exposed to more nuclear radiation than those who live at lower elevations. Those who live in areas with many rocks are exposed to more nuclear radiation than those in areas with few rocks. Radiation Exposure per Location Location Radiation exposure (millirems/year) Location Radiation exposure (millirems/year) Tampa, FL 63.7 Portland, OR 86.7 Richmond, VA 64.1 Rochester, NY 88.1 Las Vegas, NV 69.5 Wheeling, WV 111.9 Los Angeles, CA 73.6 Denver, CO 164.6 Some activities increase a person s exposure to nuclear radiation. Some of these activities are shown in the table below. Radiation Exposure per Activity Activity Smoking 1 1/2 packs of cigarettes 8,000 per day Flying for 720 hours (airline crew) 267 Radiation exposure (millirems/ year) Inhaling radon from the environment 360 Giving or receiving medical X rays 100 Interactive Reader 222 Nuclear Changes
What Are Some Beneficial Uses of Nuclear Radiation? Radioactive substances are used in many different ways. Some uses of nuclear radiation include medical diagnosis and treatment, smoke detectors, manufacturing, and agriculture. Small radioactive sources in smoke detectors release alpha particles. The charged alpha particles produce an electric current. When there is a fire, smoke particles reduce the flow of electric current. This drop in current sets off the alarm. 4. Identify What type of radiation is used in a smoke detector? TREATING CANCER Doctors can treat some cancers with controlled doses of nuclear radiation. This is known as radiotherapy. For example, some brain tumors can be treated with small beams of gamma rays. Thyroid cancer can be treated with an iodine isotope. Leukemia treatments also use radiotherapy. Large doses of nuclear radiation are used to kill defective bone marrow in leukemia patients. Then the patient can receive healthy bone marrow from a donor. 5. Infer Why do you think the beams of gamma rays used to treat brain tumors must be focused carefully? DETECTING DISEASE Nuclear radiation is used in much of the medical equipment that doctors use to detect disease. For example, CT scans show bones and dense tissue. PET scans use radioactive tracers to show how organs function. Radioactive tracers are radioactive isotopes with short half-lives that are added to a substance. Doctors can use tracers in the human body to locate tumors. Interactive Reader 223 Nuclear Changes
Doctors can use PET scans to detect disease. However, scientists can also use PET scans to study how the brain works. 6. Identify What are two uses for PET scans? AGRICULTURAL RESEARCH Scientists also use radioactive tracers in agricultural research. For example, scientists can add radioactive tracers to flowing water and study where and when the tracers reappear. This can tell them how fast water moves through soil or through the stems and leaves of crops. 7. Identify How is nuclear radiation harmful to living things? What Are Some Risks of Nuclear Radiation? Nuclear radiation has many benefits, but there are also risks. For example, nuclear radiation can be harmful to living tissue. Nuclear radiation can change the number of electrons in the molecules of living materials. This process is known as ionization. Ionized molecules may form substances that are harmful to life. The risk of damage from nuclear radiation depends on two main factors: the type of radiation and the amount of radiation exposure. EFFECT OF RADIATION TYPE Recall that different types of nuclear radiation can pass through different materials. For example, a layer of clothing or one inch of air is enough to stop alpha particles. However, beta particles are lighter and faster than alpha particles. Beta particles can pass through several feet of air or thin samples of solids and liquids. Several feet of material may be needed to protect people from high-energy gamma rays. Interactive Reader 224 Nuclear Changes
EFFECT OF EXPOSURE AMOUNT Low levels of nuclear radiation may not have a large effect on living cells. However, studies have shown that a link between cancer and exposure to high levels of nuclear radiation. RADIATION SICKNESS Exposure to high levels of nuclear radiation can cause radiation sickness. This sickness may be caused by a single large exposure, such as a nuclear explosion. Radiation sickness may also be caused by many exposures to high levels of nuclear radiation over time. People who work with nuclear radiation wear dosimeters. A dosimeter is a device that measures the amount of nuclear radiation exposure. 8. Identify What is the function of a dosimeter? A dosimeter contains a piece of film that detects radiation in the environment. RADON GAS Radon is produced by the decay of uranium-238, an isotope found in soil and rock. Radon gas emits alpha particles and gamma rays. Studies have shown that people who have been exposed to radon gas have a greater risk of developing lung cancer. The risk is even higher for people who smoke. Some areas have higher radon levels than others do. Tests for radon gas in homes and office buildings are widely available. Installing vents that draw air out of a building can help reduce high levels of radon. Sealing cracks in building foundations can also help reduce radon levels. 9. Describe How does smoking change the risk of cancer for a person exposed to radon gas? Interactive Reader 225 Nuclear Changes
How Can We Use Nuclear Power? Dozens of countries use nuclear reactors, such as the one in the figure below, to generate electricity. Energy produced from nuclear fission is used to provide electrical energy to millions of homes and businesses. Nuclear reactors are used in many parts of the world to generate electricity. 10. Describe How does the energy in uranium reserves compare to those of coal and oil? 11. Identify What is one reason nuclear power plants are expensive to build? ADVANTAGES OF NUCLEAR FISSION There are many advantages to using nuclear fission as a source of energy. Nuclear fission does not produce gases that pollute the air. There is more energy in known uranium reserves than in known gas and oil reserves. DISADVANTAGES OF NUCLEAR FISSION There are also disadvantages to using nuclear fission as a source of energy. Radioactive products of fissions may escape into the environment and spread nuclear radiation. Nuclear reactors need many safety features. Thus, nuclear power plants are expensive to build. Interactive Reader 226 Nuclear Changes
STORING NUCLEAR WASTES Nuclear wastes, such as the fuel rods that were used in the reactor, cannot simply be thrown away. Radioactive wastes must be stored safely for thousands of years until they have decayed to less harmful elements. Storage facilities must be well shielded so that nuclear radiation does not leak out and harm living things. An ideal place for storing nuclear wastes would have few people. It would also have little surface water, such as ponds, rivers, or groundwater. The area must also be free from earthquakes. 12. Explain Why must radioactive wastes be stored safely for thousands of years? Radioactive waste collection facility Storage tunnel 13. Analyze Why do you think an ideal place to store nuclear waste would be an area without earthquakes? Storage facilities for nuclear wastes must be able to contain radioactive materials safely for thousands of years. NUCLEAR FUSION Recall that energy in stars, such as our sun, is produced by fusion. Scientists are looking for ways to use fusion as an energy source here on Earth. Nuclear fusion releases very large amounts of energy, and the reaction releases very little waste or pollution. However, a large amount of energy is needed to start a fusion reaction. Thus, nuclear fusion reactions are difficult to produce in a laboratory. With current technology, the use of fusion as an energy source is not practical. 14. Explain Why are nuclear fusion reactions difficult to produce in a laboratory? Interactive Reader 227 Nuclear Changes
Section 3 Review SECTION VOCABULARY background radiation the nuclear radiation that arises naturally from cosmic rays and from radioactive isotopes in the soil and air radioactive tracers a radioactive material that is added to a substance so that its distribution can be detected later rems the quantity of ionizing radiation that does as much damage to human tissue as 1 roentgen of high-voltage X rays does 1. Identify List three activities that add to an individual s exposure to radiation. 2. Describe How do smoke detectors use nuclear radiation to detect a fire? 3. Identify What two factors determine the risk of damage from nuclear radiation? 4. Infer Why is it important to use low levels of nuclear radiation for detection and treatment of diseases? 5. Describe What are two ways to reduce the levels of radon gas in a building? 6. Identify What are two advantages and two disadvantages of using nuclear fission to generate electricity? Interactive Reader 228 Nuclear Changes