Figure 15 Gamma rays emitted by radioactive tracers in the brain are used to produce color-coded images. Areas of high activity show up in red. These images show where the brain is active when the patient is (from left to right) looking at something, listening, speaking, and thinking and speaking. The more involved the task, the more parts of the brain are activated.
Gamma Rays
Gamma rays have the shortest wavelengths in the electromagnetic spectrum, about 0.005 nanometer or less. They have the highest frequencies and therefore the most energy and the greatest penetrating ability of all the electromagnetic waves. Exposure to tiny amounts of gamma rays are tolerable, but overexposure can be deadly. 
Gamma rays are used in the medical field to kill cancer cells and make pictures of the brain, and in industrial situations as an inspection tool.
Gamma rays are used in radiation therapy to kill cancer cells without harming nearby healthy cells. Gamma rays are also used to make pictures of the human brain, with different levels of brain activity represented by different colors. Four brain scans are shown in Figure 15.
Pipelines are checked with machines that travel on the inside of a pipe, taking gamma ray pictures along the entire length. Technicians examine the pictures for rusting, cracks, or other signs of damage.
Section 18.2 Assessment
Reviewing Concepts
- List the kinds of waves included in the electromagnetic spectrum, from longest to shortest wavelength.
- Name three uses for each type of wave.
How is radar used to determine the speed of a car?
How can X-rays make pictures of the inside of solid objects?
Critical Thinking
Comparing and Contrasting How are AM radio waves similar to FM radio waves? How are they different?
Classifying What type of electromagnetic wave are microwaves and radar?
Predicting Which do you think will penetrate farther into a block of lead, X-rays or gamma rays? Explain your reasoning.
Writing in Science
Explanatory Writing Write one paragraph each about three different kinds of electromagnetic waves that you will encounter today. Use a single characteristic, such as wavelength or frequency, to describe each wave. Explain how life might be different without each kind of wave.
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