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Nuclear Fission and Fusion
Chapter 7.2Mrs. Chilton
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Nuclear Stability
• Some elements have isotopes that are stable, while others are unstable and radioactive– Example: C-12 -> stable– C-14 -> unstable, radioactive, gives off beta
particles
• Depends on nuclear forces holding nucleus together
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Strong Nuclear Force
• How do like charges act?
• They repel!
• So, why does the nucleus with so many p+ stay together?
• Strong nuclear force – stronger force than electric repulsion, but only over a short distance
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Neutrons & Stability
• Neutrons add to the stability of a nucleus
• They have no charge, so they do not repel
• Too many or too few neutrons leads to decay
• All nuclei with 83 or more protons are unstable
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Fission
• When a nucleus splits into two or more smaller fragments
• Neutrons and energy are released
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Fission -> Chain Reaction
• One neutron can split the nucleus of an atom
• As that nucleus undergoes fission, it releases more neutrons which can strike nearby atoms, causing them to split
• This can cause a chain reaction
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Nuclear Chain Reaction
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Uncontrolled chain reactions
• This principle is used in nuclear bombs• Two or more masses of U-235 are
contained in bomb surrounded by powerful explosive
• When detonated, fission chain reaction occurs releasing LARGE amount of energy which causes devastation to environment and life forms
• Fortunately, concentration of U-235 in nature is too low to start a chain reaction, most is more stable form of U-238
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Controlled Chain Reaction
• Not all neutrons released in a fission reaction succeed in triggering fission reaction
• Materials that absorb neutrons can be used to slow chain reaction
• Concept is used in nuclear power plants to generate energy
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Nuclear Reactor
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Fusion
• Energy can also be obtained when two lighter nuclei fuse together to form a larger nucleus
• In stars, including our sun, energy is produced when hydrogen nuclei undergo fusion and release TREMENDOUS amounts of energy
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Fusion in the Sun
• Multi-step process where two different isotopes of hydrogen fuse together to form a helium nucleus and energy in form of gamma rays
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Dangers of Nuclear Radiation
• Changes structure of hemoglobin
• Changes structure of macromolecules in body – health is affected
• Particles ingested through food can damage linings of organs
• Destroys bone marrow• Lung cancer (Radon gas)• Genetic mutation
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Beneficial Uses of Nuclear Radiation
• Smoke alarms –produce alpha particles to create electric current
• Controlled doses are used to treat some cancers – beams of gamma rays
• Radioactive tracers
• Nuclear power – much less pollution, more efficient (waste must be dealt with, though)
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Radioactive Waste Disposal