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Unit 4 Lesson 3 Nuclear Reactions

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New Identity What happens during a ? • A nuclear reaction is a change that affects the nucleus of an . It differs from a in several ways.

• One difference is that chemical reactions do not change the of , but nuclear reactions do so by a very small amount.

• A small amount of mass can change into a large amount of , because energy is equal to mass times the speed of squared.

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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 in the nucleus.

• Nuclear reactions that change the number of do not change an atom into a new element.

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What happens during a nuclear reaction? • Atoms with the same number of protons but different numbers of neutrons are called .

• Isotopes of the same element have different mass numbers.

• The is added to the end of the name of an element to identify isotopes, such as -6 and lithium-7.

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

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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 .

• Unstable nuclei continue to decay until they form stable nuclei. Three kinds of radioactive decay are , , and gamma decay.

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What are the types of radioactive decay? • Alpha decay is the release of an and energy from a radioactive nucleus.

• An alpha particle consists of two protons and two neutrons. It is the same as a nucleus.

• Alpha decay produces atoms of a different element because it reduces the number of protons in the nucleus.

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What are the types of radioactive decay? • Beta decay is the release of a and energy. There are two types of beta particles: and .

• Both particles have a mass of almost zero. Positrons have a charge of 1+; electrons have a charge of 1−.

• A can break apart into a and a . A neutron can break apart into a proton and an .

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What are the types of radioactive decay? • What is happening in each of these nuclear reactions?

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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 .

• Some of the energy released during alpha decay and beta decay is in the form of gamma rays.

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How does radioactive decay affect ? • 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 to radiation sickness and cancer.

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How is radioactive decay used?

• Many smoke detectors contain a small amount of radioactive . 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.

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How is radioactive decay used?

• Scientists use radioactive isotopes to determine the age of artifacts, remains, , 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.

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Radioactive Decay in Medicine

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 , such as a radioactive isotope of , helps doctors find tumors in bones. The tracer builds up in bones.

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Breaking Up What is ?

• 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.

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What is nuclear fission?

• What happens to the nucleus when it is hit by a neutron?

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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.

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What is the source of ?

• Uranium-235 is the 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 .

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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.

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How do nuclear power plants work?

• In a , 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.

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How do nuclear power plants work?

• How is nuclear energy converted to electricity?

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How can we evaluate nuclear power?

• Advantages: Nuclear fission produces a large amount of energy from a small amount of fuel. Thus, the cost of fuel is less than for a fuel power plant.

• Also, unlike fossil , nuclear energy does not pollute the air or produce greenhouse gases.

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How can we evaluate nuclear power?

• Disadvantages: Accidents at nuclear power plants may cause radioactive materials to leak out, harming the environment, including living things.

• Also, nuclear energy is not renewable, as supplies of uranium are limited.

• In addition, nuclear power plants produce , which could give off high levels of radiation for thousands of years.

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Superstars! What is fusion?

• The energy given off by the and other comes from .

• 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.

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What is fusion?

• Explain what happens during this fusion reaction.

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How can we evaluate power from fusion? • Challenges: 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.

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How can we evaluate power from fusion? • Potential benefits: The hydrogen fuel needed is readily available from the water in ’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.

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