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Nuclear Radiation
Nuclear Fission and Fusion
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Energy can be obtained two ways
Fission Splitting atoms Get energy if the nucleus is big. The smaller ones are more stable. What we do in nuclear reactors.
Fusion Joining atoms Get energy if the nuclei are small. The larger one is more stable. This is how the sun works.
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Nuclear Fission
Fission is the splitting of atoms These are usually very large, so that they are
not as stable Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts
the chain (e.g., 235U + neutron) 2. Propagation. 236U fission releases
neutrons that initiate other fissions 3. Termination.
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Nuclear Fission
A very heavy nucleus splits into more stable nuclei of intermediate mass.
The mass of the products is less than the mass of the reactants.
Missing mass is converted to energy
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In nuclear fission,
• a large nucleus is bombarded with a small particle.
• the nucleus splits into smaller nuclei and several neutrons.
• large amounts of energy are released.
Nuclear Fission
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When a neutron bombards 235U,
• an unstable nucleus of 236U undergoes fission (splits).• smaller nuclei are produced such as Kr-91 and Ba-142.• neutrons are released to bombard more 235U.
1n + 235U “236U” 91Kr + 142Ba + 3 1n +
0 92 92 36 56 0
Nuclear Fission
Energy
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Nuclear Fission Diagram
1n + 235U “236U” 91Kr + 142Ba + 3 1n + energy 0 92 92 36 56 0
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Where does all this energy come from?
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E = mc2E = Energy (joules)m = mass (kg)c = speed of light = 3 x 10^8 m/s
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Learning Check
Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction.
1n + 235U 137Te + ?X + 2 1n + energy0 92 52 ? 0
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Solution
1n + 235U 137Te + 97Zr + 2 1n + energy0 92 52 40 0
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Chain Reaction
A chain reaction occurs
• when a critical mass of uranium undergoes fission.
• releasing a large amount of heat and energy that produces an atomic explosion.
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Nuclear Power Plants
In nuclear power plants, • fission is used to produce energy.• control rods in the reactor absorb neutrons to
slow and control the chain reactions of fission.
Fusion
Light-mass nuclei combine to form a heavier, more stable nucleus.
More energetic than fission reactions
Source of energy for the H-bombOrigin of the elements
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The most destructive force on the planet
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H-bombs 1000s of times more powerful than A-bombs
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Nuclear Fusion
Fusion• occurs at extremely high temperatures (100 000 000°C).• combines small nuclei into larger nuclei.• releases large amounts of energy.• occurs continuously in the sun and stars.
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Fusion: small nuclei form larger nuclide, release energy
This type of Fusion is beingExamined asAn alternativeEnergy sourceOn Earth.
Small nuclei come together to form larger nuclide, releasing energy
Fusion of Helium atoms
4 2He + 4 2 He ? + energy
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Fusion of Helium atoms
4 2He + 4 2He 8 4Be + energy
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Practice
4 2He + 8 4Be ? + energy
4 2He + ? 16 8O + energy
4 2He + 16 8O ? + energy
4 2He + 20 10Ne ? + energy
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Answers
4 2He + 8 4Be 12 6C + energy
4 2He + 12 6C 16 8O + energy
4 2He + 16 8O 20 10Ne + energy
4 2He + 20 10Ne 24 12Mg + energy
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Indicate if each of the following describes1) nuclear fission or 2) nuclear fusion.
___ A. a nucleus splits. ___ B. large amounts of energy are released.___ C. small nuclei form larger nuclei.___ D. hydrogen nuclei react.___ E. several neutrons are released.
Learning Check
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Indicate if each of the following is1) nuclear fission or 2) nuclear fusion.
1 A. a nucleus splits. 1, 2 B. large amounts of energy are released. 2 C. small nuclei form larger nuclei. 2 D. hydrogen nuclei react. 1 E. several neutrons are released.
Solution
