Unit 4 Lesson 3 Nuclear Reactions
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New Identity
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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.
Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
What happens during a nuclear reaction?
• Compare and contrast the isotopes lithium-6 and lithium-7.
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Unit 4 Lesson 3 Nuclear Reactions
Just Passing Through
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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.
Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
What are the types of radioactive decay?
• What is happening in each of these nuclear reactions?
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
Unit 4 Lesson 3 Nuclear Reactions
Radioactive Decay in Medicine
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• 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.
Breaking Up
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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.
Unit 4 Lesson 3 Nuclear Reactions
What is nuclear fission?
• What happens to the uranium nucleus when it is hit by a neutron?
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Unit 4 Lesson 3 Nuclear Reactions
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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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
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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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
How do nuclear power plants work?
• How is nuclear energy converted to electricity?
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Unit 4 Lesson 3 Nuclear Reactions
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 fossil fuel power plant.
• Also, unlike fossil fuels, nuclear energy does not pollute the air or produce greenhouse gases.
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Unit 4 Lesson 3 Nuclear Reactions
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 radioactive waste, which could give off high levels of radiation for thousands of years.
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Unit 4 Lesson 3 Nuclear Reactions
Superstars!
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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.
Unit 4 Lesson 3 Nuclear Reactions
What is fusion?
• Explain what happens during this fusion reaction.
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions
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.
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Unit 4 Lesson 3 Nuclear Reactions