Download Chapter 16 Atomic Energy

Chapter 16 Atomic Energy
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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.
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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.
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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.
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Chapter 16 Atomic Energy
What happens during a nuclear
reaction?
• Compare and contrast the isotopes lithium-6 and
lithium-7.
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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.
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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.
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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.
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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?
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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.
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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.
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Chapter 16 Atomic Energy
How does radioactive decay affect
matter?
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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.
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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.
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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.
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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.
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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.
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Chapter 16 Atomic Energy
What is nuclear fission?
• What happens to the uranium nucleus when it is
hit by a neutron?
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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.
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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.
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Chapter 16 Atomic Energy
What is the source of nuclear power?
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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.
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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.
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Chapter 16 Atomic Energy
How do nuclear power plants work?
• How is nuclear energy converted to electricity?
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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.
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Chapter 16 Atomic Energy
What is fusion?
• Explain what happens during this fusion reaction.
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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.
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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.
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