Nuclear Fission and
Fusion
UMA LAD
P HY 3 3 0 5: MODE R N P HYS I CS
DECE MBE R 2 , 2 0 1 4
Outline
• Fission and fusion will be defined.
• Examples of fission and fusion will be discussed.
• Modern day applications of these reactions will be discussed.
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Nuclear Reaction
• Occurs when a nucleus collides with another particle
• Example: uranium- 235 decays into barium and krypton
Total Energy released:
Q= (mi – mf)c2
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Nuclear Fission
• Nucleus breaks down into many
parts
• Releases kinetic energy
• Many isotopes decay through
induced fission
• Number of protons and neutrons
affects the amount of energy
released
Fig. 1. Uranium Fission. “Mousetrap Reactor.” SMU Physics and
Astronomy Demonstrations. 2014. Web. 25 Nov. 2014.
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Chain Reactions
• Each fission reaction will cause other fission reactions to occur.
• Critical assembly: ensures that a reaction can sustain itself
The energy released during a chain reaction:
Ej = E0kj
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Fission Reactor
• Uranium-235 is used as the fuel
• Control rods absorb neutrons
• Neutrons produced from each generation become slower
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Pressure Water Reactor
Fig. 2. A Light-Water Nuclear Fission Reactor for the Production of Electric Power. Digital image. ”Applied Nuclear Chemistry.” UC Davis Chemwiki.
UC Davis, n.d. Web. 20 Nov. 2014.
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Nuclear Fusion
•
Nuclei combine to form heaver nuclei
• Mass decreases
• Kinetic energy increases
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Lawson Criterion
• For fusion to occur:
• High temperatures are necessary
• Reaction must be held:
• For a certain amount of time
• A certain density of ions
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Proton-Proton Cycle
• End result: helium
• Energy source of the Sun
Fig. 3. Fission in the Sun. “Proton- Proton Chain Reaction.”
Wikipedia. Wikimedia Foundation Inc., 2006. Web. 25 Nov. 2014.
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Fusion in Relation to Stars
• Carbon Cycle
•
Uses carbon as a catalyst
•
Results in helium
•
Occurs when a star has a high temperature
• Stellar Collapse- Star collapses into a white dwarf
•
Energy production from fusion no longer matches the gravitational
attraction
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Fusion Reactors
• Difficult to use as a power source
• Requires extreme conditions
• Ways to confine nuclei
• Magnetic confinement
• Inertial confinement
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Conclusion
• Fission - nucleus breaking down into many parts.
• Fusion - nuclei combining to form heaver nuclei.
• Chain reaction - one reaction triggers many other reactions.
• Fission reactors are used to produce energy.
• Proton-proton cycle is composed of multiple fusion reactions.
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Sources
Harris, Randy. Modern Physics. 2nd ed. San Francisco: Pearson, 2008. 503-513. Print.
Herrmann, Mark. “Plasma Physics: A promising advance in nuclear fusion.” Nature 506 (2014):
302-303. Web. 17 Nov. 2014.
Nave, Rod. "Nuclear Fusion." HyperPhysics. Web. 11 Nov. 2014. <http://hyperphysics.phy-astr.
gsu.edu/hbase/nucene/fission.html#c1>.
Reed, Cameron B. “Neutrons as Party Animals: An Analogy for Understanding Heavy-Element
Fissility.” The Physics Teacher 50 (2012): 544-545. Web. 17 Nov. 2014.
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