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The most common, and one of the earliest uses of radiation, is to diagnose injury and disease. Roentgen's discovery of the xray allowed physicians to look inside the human body without operating.

Figure 13. Use of X-ray Machine in Medicine

Today, doctors also use radiation in many ways to treat disease. One of every three Americans hospitalized each year is diagnosed or treated using nuclear medicine,totaling more than 11 million procedures a year. Radiation is also used in 100 million laboratory tests each year on body fluids and tissue specimens to aid in diagnosing disease.

Ionizing radiation is widely used to diagnose and treat cancer,increasing survival rates and improving patients' quality of life. Radiotherapy has helped to cure various types of cancer in tens of thousands of people and temporarily to halt the disease in many others. About 500,000 cancer patients in the United States — half of all people with cancer— are treated with radiation at some point in their therapy.

For example, a promising treatment for leukemia involves arming monoclonal antibodies with radioisotopes. The antibodies are produced in the laboratory and engineered to bind to a specific protein in tumor cells. When injected into a patient, these armed antibodies bind to the tumor cells, which are then killed by the attached
radioactivity. Normal cells nearby are not affected.

Other applications of radiation in cancerdiagnosis and treatment include:

• Mammography to detect breast cancer at an early stage when it may be curable
  
• X-rays or other imaging techniques that make needle biopsies safer and more accurate and informative
  
• Monitoring the response of tumors to treatment, and distinguishing malignant from benign tumors
  
• Bone and liver scans to detect the spread of cancers
  
• Alleviating or eliminating pain associated with prostate or breast cancer that has spread to the bones
  

The National Institutes of Health (NIH) lists more advanced medical uses of radiation:

Figure 14. CAT Scan

• Newer xray technologies such as computerized tomography (CT, or CAT) scans have revolutionized the diagnosis and treatment of diseases affecting almost every part of the body. (Figure 14)
  
  
• Another scanning technology, positron emission tomography (PET) scanning, involves injecting a small amount of a radioisotope into a patient to show the metabolic activity and circulation in the brain. PET studies enable scientists to pinpoint the site of brain tumors or the source of epileptic activity and to better understand many neurological diseases.
  
  
• Radioisotopes are used to diagnose and monitor many diseases effectively and safely. To show how the disease process alters the normal function of an organ, a patient swallows, inhales, or receives an injection of a tiny amount of a radioisotope. Special cameras reveal where the isotope accumulates in the body (for example, showing an image of the heart with both normal and malfunctioning tissue).
  
  
• Laboratory tests use radioisotopes to measure important substances in the body, such as thyroid hormones.
  
  
• Radiation treatments for thyroid diseases, including thyroid cancer and Graves disease (one of the most common forms of hyperthyroidism), are so effective they have almost totally replaced thyroid surgery.
  
  
• Radioisotopes are used in animal studies to learn how the body metabolizes a new drug before it is approved by the Food and Drug Administration (FDA).
  
  
• Radioisotopes are used to sterilize hospital items to help prevent the spread of diseases. Radiation is especially useful for sterilizing such items as sutures, syringes, catheters, and hospital clothing that would otherwise be destroyed by heat sterilization. Sterilization using radioisotopes is particularly valuable because it can be performed while the items remain in their sealed packages, thus preserving their sterility indefinitely.
  
  
• Radioisotopes are a technological backbone of biomedical research. They are used to identify how genes work, and in much of the research on AIDS. Between 70 and 80 percent of all research at NIH is performed using radiation and radioactive materials.

Industry

Numerous businesses and industries have found uses for radiation to improve products or services. The Nuclear Regulatory Commission (NRC) and the 32 states that participate in the NRC Agreement States program issue and administer more than 20,000 licenses for medical, academic, and industrial uses of nuclear materials. Manmade radioisotopes are used by industry to:

• Explore for oil and natural gas. Geologists use a technique called nuclear well logging to determine whether a well drilled deep in the ground has the potential to produce oil. Radiation from a radioisotope inside the well can detect the presence of different materials.
• Test pipes and welds, including structural cracks and stresses in aircraft (Figure 15) and test for flaws in jet engines. Using a process called radiography, the object tested is exposed to radiation from a sealed radiation source and a piece of photographic or radiographic film on the opposite side of the object captures an image which can help to pinpoint flaws such as cracks or breaks.

  Figure 15. Airplane

• Control the thickness of sheet products, such as steel, aluminum foil, paper, photographic film, and plastics, during manufacture. Detectors measure, highly accurately, the amount of radiation passing through the materials and compare it to the amount that should pass through the desired thickness.
  
  
• Cold-sterilize plastics, pharmaceuticals, cosmetics, and other heat-sensitive products. Exposing the materials to radiation, usually gamma radiation from Cobalt-60, kills bacteria and germs and is particularly effective when other methods such as boiling or chemical treatment are not practical.
  
  
• Conduct security checks of airline carry-on luggage.
  
  
• Improve the quality of manufactured goods in thousands of industrial plants by using radiation in sensitive gauges and imaging devices (for example, ensuring that beverage cans are correctly filled using a process similar to that of measuring the thickness of sheet products).
  
  
• Pinpoint fluid leaks, monitor engine wear and corrosion, and measure the flow of materials through pipes, using radioactive tracers similar to those used in medicine.
  
  
• Identify trace quantities of materials. Criminal investigators use radiation to identify trace amounts of materials like glass, tape, gunpowder, lead, and poisons. Called activation analysis, the procedure involves placing a sample of materials in a nuclear reactor and bombarding it with neutrons, which produces a "fingerprint" of the elements in the sample.
  
  
• Prove the authenticity of old paintings. Museums also use activation analysis to detect whether certain modern materials are present and use other techniques with radioisotopes to spot forgeries.
  
  
• Detect pollution. Scientists use radioisotopes to trace and identify the sources of pollution, such as acid rain and greenhouse gases, in air, water, and soil.

One-sixth of the world's electricity, and nearly one-fifth of the electricity in the United States, comes from nuclear power plants. (Figure 16) These plants use nuclear fission (neutrons splitting uranium atoms) to produce tremendous heat that generates electricity. Americans get more of their electricity from nuclear power than from any other source except coal.

Figure 16. Nuclear Power Plant

But nuclear power plants also have a number of drawbacks. U.S. nuclear power plants generate about 2,000 metric tons of high-level radioactive waste each year, causing significant disposal problems. (See Nuclear Reactor Waste).

Environmental and antinuclear groups oppose nuclear power because of concerns about safety, the potential for nuclear weapons proliferation and terrorism, and because of the unresolved problem of nuclear waste disposal. They argue that renewable energy sources such as solar and wind power are preferable to nuclear power as long-term alternatives to fossil fuel energy. (For more on the pros and cons of nuclear power, see Balancing the Benefits and Risks.)

Some people consider nuclear power plants more environmentally friendly than coal or oil-burning plants. As a byproduct of combustion, fossil-fuel plants emit air pollutants such as nitrogen oxide, sulfur dioxide, and carbon dioxide, a principal "greenhouse gas" believed to contribute to global warming. Because nuclear plants use fission instead of combustion, they produce no combustion byproducts. Without nuclear power, U.S. carbon emissions from electric generation would be about 30 percent higher.

Also, because they are so closely regulated and monitored, nuclear power plants release less ionizing radioactivity (an average dose of 0.009 mrem per year) into the environment than comparable coal-fired plants (an average dose of 0.03 mrem per year). New limits on fly-ash emissions from fossil-fuel plants, however, are helping to reduce radioactive emissions from these sources as well.

According to the Nuclear Energy Institute, the industry's trade association, the annual economic impact of the nuclear power industry is $90 billion in total sales of goods and services; 442,000 jobs; and $17.8 billion in federal, state, and local government tax revenues. The Institute estimates that nuclear power reduces U.S. reliance on foreign sources of oil by nearly 100 million barrels a year, enhancing the nation's energy security, and cutting the U.S. trade deficit by billions of dollars each year.

Agriculture

Radiation has become an increasingly important tool in agricultural research and practice. Some uses and their benefits are:

• Radioisotopes as a research tool help develop new strains of food crops that are more nutritious, resist disease, and produce higher yields. For example, radiation has been used in producing peanuts, tomatoes, onions, soybeans, barley, and the "miracle" rice that has boosted rice production in Asia.
• Radioisotope tracers in plant nutrients aid in reducing soil and water pollution by helping researchers to learn how plants absorb fertilizer and how to calculate the optimum amount and frequency of fertilizer applications.
• Insect sterilization with radiation results in mating without offspring, thus limiting insect population growth. This has eliminated screwworm infestation in the southeastern United States and Mexico, and has helped control the Mediterranean fruit fly in California. With fewer pests, food crop productivity increases.
• Moisture monitoring with nuclear density gauges can measure the moisture content of soil, helping make the most efficient use of limited water sources for successful crop production.

Irradiation Process

One of the more controversial uses of radiation today is food irradiation. High doses of radiation do not make food radioactive. Irradiation kills bacteria, insects, and parasites, and retards spoilage in some foods. Irradiated foods are regularly eaten by astronauts on space missions, as well as by hospitalized patients with weak immune systems who need extra protection from microorganisms in food.

The irradiation process involves exposing food to intense controlled amounts of ionizing radiation ó gamma rays from cobalt-60 or cesium-137, xrays, or electron beams from particle accelerators. The process has about the same effect on food as canning, cooking, or freezing. It kills pests and extends shelf life, but also reduces the food's nutritional value somewhat by destroying vitamins A, B1 (thiamin), C, and E. No radiation remains in the food after treatment.

Exposing materials, including foods, to radiation from an irradiator is very different from exposing them to radiation from a reactor. The gamma radiation from cobalt-60 in an irradiator kills bacteria and germs, but does not leave any radioactive residue or cause any of the exposed materials to become radioactive. The cobalt-60 in an irradiator is contained in stainless steel capsules and does not commingle with the material being irradiated. On the other hand, material exposed to neutrons from a reactor or linear accelerator can become radioactive.

Approvals and Bans
Irradiation has been approved by:

• The FDA ó for a number of foods including, herbs and spices, fresh fruits and vegetables, wheat, flour, pork, poultry, and red meat
• The World Health Organization
• The United Nations Food and Agricultural Organization
• Approximately 40 countries besides the United States

Three states ó Maine, New Jersey, and New York ó have banned the sale, however, of irradiated foods and food ingredients (except for spices). Many U.S. food producers have been reluctant to adopt food irradiation because of protests by food-safety groups and because of uncertainties about consumer acceptance.

Benefits
Irradiation advocates, including the FDA and the U.S. Department of Agriculture (USDA), point to a number of benefits of food irradiation:

• The process is better for the environment than treating foods with toxic chemicals, such as methyl bromide or ethylene oxide.
  
  
• Irradiation, coupled with proper handling, cooking, and storage of food, can help reduce the incidence of food-borne disease. Some six million cases a year in the United States result in more than 9,000 deaths.
  
  
• By retarding spoilage and extending the shelf life of food, irradiation also helps humanitarian groups deliver food to starving people.
  
  

Concerns
However, critics point to a number of concerns with food irradiation:

• Irradiated foods could pose a botulism hazard because the process kills bacteria that cause spoiled food to smell or look bad, thereby eliminating the traditional signals of inedible food.
• Irradiation can accelerate spoilage in several fruits, including pears, apples, citrus fruits, and pineapples.
• The irradiation process may expose workers and the environment to radiation hazards.
• Irradiation reduces the food's nutritional value by destroying some vitamins.

While extensive studies have found no evidence that irradiated foods or compounds cause adverse health effects, some consumers may find them unacceptable because they prefer natural or organic foods.

How do you know if the food in your grocery store has been irradiated?
The FDA requires irradiated foods to be labeled with the green radiation logo, called the radura (Figure 17) and the words "treated by irradiation," "treated with irradiation," or "irradiated."

Figure 17. Radura Label

However, processed foods containing irradiated ingredients and irradiated food sold in restaurants do not have to be labeled. Consumer groups are working to expand the labeling requirement.

Should you avoid irradiated food?

If your only concern is possible adverse health effects, the government says no.

• The FDA has found no evidence that irradiation of food is less safe than other preservation methods.
• Irradiation does a good job of killing bacteria that cause food-borne diseases such as, salmonella in poultry and seafood, E. coli in beef, trichinosis in pork, and cholera in fish.

But if it is more important to you that your foods are grown and packaged naturally without artificial treatments and with their vitamins and minerals intact, then irradiated foods may not be prime candidates for your shopping list.

Consumer Products

Radiation is used in, or to produce many consumer products. For example, many smoke detectors — now installed in nearly 90 percent of American homes — use the radioactive isotope americium-241, which emits alpha radiation. By ionizing the air sealed inside the detector, the radiation produces an electric current that sets off the alarm if interrupted by smoke in the detector.

Radioactive materials are also used to:

• Eliminate dust from computer disks and audio and video tapes
  
• Sterilize baby powder, bandages, cosmetics, hair products, and contact lens solutions (Exposing these materials to radiation, usually gamma radiation from cobalt-60 kills bacteria and germs.)
• Control the thickness of many sheet products, such as paper, sandpaper, or aluminum foil and the amount of liquid in beverage can (Detectors measure, highly accurately, the amount of radiation passing through the materials and compare it to the amount that should pass through the desired thickness.)
• Attach a non-stick surface to a frying pan
• Brighten the porcelain in false teeth to make them look more real

None of the radiation remains in these consumer products after they are treated or sterilized.

Radioactive materials also create the glow in luminous watches and in instrument panel dials and are used in some gas camping lanterns. Radiation is also used in production of some clothing, eyeglass lenses,
lightning rods, tires, ceramic glazes on some china and decorative glassware, enameled
jewelry, and cellophane dispensers.

Only a small fraction of our total annual exposure to radiation, about 11 millirem a year, comes from consumer products.

The Space Program

The U.S. Space Program has used radioisotope thermoelectric generators (RTGs) to power 24 of its space probes over the last 25 years. The natural decay of plutonium dioxide produces heat, which is converted to electricity by a thermocouple device. Compact and relatively light, RTGs typically produce about 300 watts of electricity and can operate unattended for years.

Among the space research probes powered by RTGs were:

• The Apollo Lunar Surface Experiment Packages (1969-1971)
• Pioneer 10 and 11 (1972 and 1973)
• Two Viking Mars spacecraft (1978)
• Two Voyager spacecraft (1977)
• The Galileo (1989), Ulysses (1990), and Cassini (1997) spacecraft.

The U.S. Navy was an early user of nuclear power, launching the USS NAUTILUS, the first nuclear-powered submarine, in 1954. Since 1954, the Navy has built more than 200 submarines and surface ships powered by nuclear reactors. These vessels have traveled more than 100 million miles of ocean on nuclear power.

Nuclear submarines have two major advantages: speed and underwater range without surfacing. A modern nuclear powered Navy submarine can cruise up to one million miles, or more than 25 years, without refueling.

Research

Radioactive materials are valuable tools for research in nearly all fields of modern science: physics, mineralogy, metallurgy, biology, medicine, agriculture, environmental science, geology, chemistry, and many others.

• Many scientists use xrays and neutrons to study the properties of a wide variety of materials, develop new plastics, and strengthen materials, such as those used in aircraft.
  
  
• Chemists and biologists use xray diffraction techniques to study the crystalline structure of proteins, the basic building blocks of life, and also to study viruses that cause diseases ranging from the common cold to AIDS.
  
  
• Environmental scientists use radioisotopes to track chemical contaminants as they move through water or the ground and to study the global movement of wind and water.
  
  
• Geologists read radioactive materials that occur naturally in the Earth to determine the age of rocks and to study plate tectonics.
  
  
• Archaeologists determine the age of prehistoric artifacts through carbon dating, a process that measures radioactive carbon-14. When an organism is alive, its ratio of carbon-14 to carbon-12 is the same as in the atmosphere. When the organism dies, the carbon-14 begins to decay and the ratio changes. This ratio is used to determine how long ago the organism died.
  
  
• Criminologists use neutron activation analysis to detect the presence of toxic substances such as arsenic in the body.
  
  
• Investigators detect forgeries by measuring radioactive decay; and use "ultrasoft" X-rays to determine the authenticity of paintings and to aid in their restoration.