1. Fusion and Fission Reactions
Atomic Physics

2. Fission splitting of a nucleus into two smaller nuclei
nucleus must have an atomic mass A > 120
the energy difference of binding energy is the energy released in the reaction

3. Energy released

4. Fission
Many fission reactions are initiated by a free neutron colliding with a nucleus to form an unstable isotope.
The unstable nucleus breaks up almost instantly into smaller nuclei.

5. Eg) Fission of Uranium-235
High energy neutron
collides
Barium -141
Krypton - 92
+ energy
This energy is released by each
atom that reacts.

6. Chain reaction Note that the example fission reaction emits 3 n°.
Each n° can initiate additional fission reactions.
This can produce a chain reaction.

7. Chain Reaction Video http://www.youtube.com/watch?v=Pmy5fi vI_4U
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Big Boom
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8. Slow boom
A nuclear reactor slows the chain reaction so that it does releases energy in a slow steady rate.
This is usually done by absorbing neutrons to prevent one reaction from initiating several new reactions.
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9. Fusion – process of combining smaller nuclei to produce a larger one with the release of energy
Involves two low mass nuclei, A < 60, resulting in a single nucleus being formed
Energy released is the difference in mass of the nuclei and individual parts
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10. Power of the Sun

11. Reaction
The proton-proton chain is a series of fusion reactions (see page 821).
The overall reaction is:
Energy released: MeV

13. Example: Fusion of Hydrogen Isotopes
Temperature of 106 ⁰C
Energy could be used to produce steam to drive a turbine and create electrical energy through the generator effect
Energy is needed to have the reaction occur to overcome the electrostatic force of repulsion between protons
Inefficient because the energy in is greater than the energy out

14. Fission vs. fusion Fission: 1 big --> 2 small nuclei
Fusion: 2 small --> 1 bigger nucleus
Fission can occur spontaneously.
Fusion requires pushing two positive nuclei together and overcoming electrostatic repulsion. (high temperatures: very fast moving atoms)

15. Nuclear power
Energy from fission reactions used to vaporize water, steam used to turn turbine, which generates electricity.
No green house gases.
Need to contain radioactivity.
Waste product radioactive, often with very long half-lives. Must be stored.

16. Power from fusion Sustained, controlled fusion reaction needed.
Not (yet) able to do this.
Much less radioactive waste (almost none usually).
Potential is almost unlimited in theory.

17. Nuclear weapons A-bomb: uses fission of uranium or plutonium
H-bomb: uses fusion of H (way bigger boom)
Hazards: huge explosion, scatters radioactive waste all over the place.

18. How to build a bomb Just kidding….
Obtain at least critical mass of weapons grade U or Pu.
Mold into two half spheres.
Use TNT to drive two half spheres together.
Boom (if you are lucky).