Chapter 16 Atomic Energy. Copyright Houghton Mifflin Harcourt Publishing Company

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2 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.

3 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.

4 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.

5 What happens during a nuclear reaction? Compare and contrast the isotopes lithium-6 and lithium-7.

6 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.

7 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.

8 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.

9 What are the types of radioactive decay?

10 What are the types of radioactive decay?

11 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.

12 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.

13 How does radioactive decay affect matter?

14 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.

15 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.

16 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.

17 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.

18 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.

19 What is nuclear fission? What happens to the uranium nucleus when it is hit by a neutron?

20 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.

21 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.

22 What is the source of nuclear power?

23 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.

24 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.

25 How do nuclear power plants work? How is nuclear energy converted to electricity?

26 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.

27 What is fusion? Explain what happens during this fusion reaction.

28 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.

29 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.