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Chapter 16 Atomic Energy Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy New Identity What happens during a nuclear reaction? • A nuclear reaction is a change that affects the nucleus of an atom. It differs from a chemical reaction in several ways. • One difference is that chemical reactions do not change the mass of atoms, but nuclear reactions do so by a very small amount. • A small amount of mass can change into a large amount of energy, because energy is equal to mass times the speed of light squared. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What happens during a nuclear reaction? • Chemical reactions do not change the nucleus of atoms, but nuclear reactions do. • Nuclear reactions can change the identity of atoms by changing the number of protons in the nucleus. • Nuclear reactions that change the number of neutrons do not change an atom into a new element. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What happens during a nuclear reaction? • Atoms with the same number of protons but different numbers of neutrons are called isotopes. • Isotopes of the same element have different mass numbers. • The mass number is added to the end of the name of an element to identify isotopes, such as lithium-6 and lithium-7. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What happens during a nuclear reaction? • Compare and contrast the isotopes lithium-6 and lithium-7. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy Just Passing Through What are the types of radioactive decay? • Radioactive decay is a nuclear reaction in which an unstable nucleus can give off energy and, sometimes, particles. • The particles and energy given off are called nuclear radiation. • Unstable nuclei continue to decay until they form stable nuclei. Three kinds of radioactive decay are alpha decay, beta decay, and gamma decay. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What are the types of radioactive decay? • Alpha decay is the release of an alpha particle and energy from a radioactive nucleus. • An alpha particle consists of two protons and two neutrons. It is the same as a helium nucleus. • Alpha decay produces atoms of a different element because it reduces the number of protons in the nucleus. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What are the types of radioactive decay? • Beta decay is the release of a beta particle and energy. There are two types of beta particles: positrons and electrons. • Both particles have a mass of almost zero. Positrons have a charge of 1+; electrons have a charge of 1−. • A proton can break apart into a neutron and a positron. A neutron can break apart into a proton and an electron. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What are the types of radioactive decay? Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What are the types of radioactive decay? Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What are the types of radioactive decay? • Gamma rays are released during gamma decay. Gamma rays are high-energy radiation and have no mass and no charge. • Gamma decay alone does not change the number of particles in the nucleus. Therefore, it does not form a different element or isotope. • Some of the energy released during alpha decay and beta decay is in the form of gamma rays. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How does radioactive decay affect matter? • Although alpha particles do not penetrate deeply, they can damage living cells by breaking apart chemical bonds when they hit substances. • Beta particles can also break molecular bonds in cells and cause illness. • Gamma rays have the greatest penetrating power. They can remove electrons from atoms, damaging cells and weakening metals. Large doses lead to radiation sickness and cancer. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How does radioactive decay affect matter? Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How long does it take for particles to decay? • Half Life is the amount of time it takes for onehalf of the nuclei of a radioactive isotope to decay. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How is radioactive decay used? • Many smoke detectors contain a small amount of radioactive americium. The americium emits alpha particles that are used to detect smoke. • Gamma rays are used to kill bacteria on bandages. • Radioactive decay is used to test the thickness of metal sheets and to find leaks in pipes. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How is radioactive decay used? • Scientists use radioactive isotopes to determine the age of artifacts, remains, fossils, and rocks. • Radioactive tracers are often used to produce images of human body parts. • Radioactive material inserted into a tumor can kill the cancer cells that make up the tumor. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy Radioactive Decay in Medicine • Positron emission tomography (PET) is often used to study brain activity. Tumors are more active than other areas. • A gamma knife is a medical device that can be used to destroy brain tumors. It delivers gamma rays to very precise areas of the brain. • A radioactive tracer, such as a radioactive isotope of technetium, helps doctors find tumors in bones. The tracer builds up in bones. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy Breaking Up What is nuclear fission? • The nuclear reaction in which a large, unstable nucleus breaks into two smaller nuclei is called nuclear fission. • Nuclear fission also releases neutrons and a large amount of energy. • Like alpha decay and beta decay, fission changes the nucleus of the atom that breaks apart. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What is nuclear fission? • What happens to the uranium nucleus when it is hit by a neutron? Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How are mass and energy conserved? • In a nuclear fission reaction, a small amount of the mass of the original nucleus is converted to energy. • The amount of energy given off by a single fission reaction is small. But a large amount of energy is produced by the fission of many atoms. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What is the source of nuclear power? • Uranium-235 is the fuel used in nuclear power plants. • When a uranium nucleus splits apart, it releases neutrons. These neutrons then hit other uranium nuclei, which split apart, too. • This continuous series of fission reactions is known as a nuclear chain reaction. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What is the source of nuclear power? Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What is the source of nuclear power? • An uncontrolled chain reaction gives off huge amounts of energy very quickly. • The nuclear explosions of atomic bombs are the result of uncontrolled chain reactions. • Chain reactions can also be controlled. Nuclear power plants turn the energy released by these controlled reactions into electrical energy. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How do nuclear power plants work? • In a nuclear power plant, the energy released during a controlled chain reaction is used to generate electrical energy. • To control the chain reaction, engineers must keep many of the released neutrons from hitting other uranium nuclei. • Control rods absorb these neutrons, limiting the number of neutrons available to continue the chain reaction. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How do nuclear power plants work? • How is nuclear energy converted to electricity? Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy Superstars! What is fusion? • The energy given off by the sun and other stars comes from nuclear fusion. • Nuclear fusion is the process by which nuclei of small atoms combine to form a new, more massive nucleus. • Fusion reactions change a small amount of mass into a large amount of energy. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy What is fusion? • Explain what happens during this fusion reaction. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How can we evaluate power from fusion? • Challenges: Hydrogen fusion takes place only at temperatures of millions of degrees Celsius. • To produce these temperatures requires a large input of energy, and no known material can sustain these high temperatures. • Currently, more energy is needed to produce the conditions needed for fusion than can be produced by the fusion reaction itself. Copyright © Houghton Mifflin Harcourt Publishing Company Chapter 16 Atomic Energy How can we evaluate power from fusion? • Potential benefits: The hydrogen fuel needed is readily available from the water in Earth’s oceans. • The fusion reaction does not produce radioactive waste or greenhouse gases. • An accident at a fusion reactor would release little nuclear radiation into the environment. Copyright © Houghton Mifflin Harcourt Publishing Company