Nuclear Fission and Fusion

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Nuclear Fission and Fusion
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Nuclear power

• Power 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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Fission

• In 1939 Lise Meitner an Austrian chemist in
  Sweden also working on neutron bombardment
  experiments proposed that the barium formed as a
  result of the neutrons splitting the Uranium
  atoms into two fragments
• She proposed the term fission to describe this
  process because of its similarity to the
  reproductive fission of a biological cell

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Fission of 238U
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Chain Reaction
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Uranium Isotopes

• Naturally occurring Uranium contains two major
  isotopes
• Uranium-238 (99.3)
• Uranium-235 (0.7)
• As it turns out the only isotope of Uranium that
  undergoes fission is Uranium-235

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235U Fission

• 23592U 10n ? 23692U
• and 10-14 seconds later...
• 23692U ? 9236Kr 14156Ba 3 10n ENERGY
• 50 possible sets of fission products (sum of
  atomic numbers 92)
• 3 neutrons released for ONE 23592U
• each neutron can split another 23592U
• CHAIN REACTION POSSIBLE
• If amount of 23592U is sufficient (CRITICAL MASS)
  then the number of neutrons generated is high
  enough to result in a nuclear explosion )

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Where does all this energy come from?
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E mc2E Energy (joules)m mass (kg)c
speed of light 3 x 108 m/s
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Nuclear Fission POWER

• Currently about 103 nuclear power plants in the
  U.S. and about 435 worldwide.
• 17 of the worlds energy comes from nuclear.

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Fusion

• Light-mass nuclei combine to form a heavier, more
  stable nucleus.
• More energetic than fission reactions
• Source of energy for the H-bomb
• Origin of the elements

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FUSION
411H ? 42He 2 ? ? energy
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The most destructive force on the planet
H-bombs 1000s of times more powerful than A-bombs
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Fusion of Helium atoms42He 42He ? ? energy
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Fusion of Helium atoms 42He 42He ? 84Be
energy
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Practice42He 84Be ? ? energy42He ? ?
168O energy42He 168O ? ? energy42He
2010Ne ? ? energy
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Answers42He 84Be ? 126C energy42He 126C
? 168O energy42He 168O ? 2010Ne
energy42He 2010Ne ? 2412Mg energy
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Binding Energy of Nuclei