Optional Unit VIII: Atomic Physics
C. Nuclear Fusion

Key Concepts

Nuclear fusion occurs within the sun and the stars.

Fusion in the sun is believed to occur in steps. Four protons produce one atom, two positrons, and two neutrinos. The first two steps shown below must occur twice before the third step takes place:

Fusion in stars produces all of the chemical elements found on Earth.

Sunlight is energy released from fusion reactions in the sun.

Examining the spectral characteristics of stars may provide a better understanding of fusion.

Fusion is believed to be possible only under extremely high temperatures. For this reason it is referred to as a thermonuclear reaction.

The use of nuclear fusion for commercial purposes is currently being investigated.

One reaction that may eventually be able to produce controlled fusion is:

Fusion has the potential of providing an abundant supply of energy. The fuel needed for fusion is readily available.

Deuterium must be extracted from water. (About 0.015% of the hydrogen in water is exists as deuterium.) Tritium () must be made, since it does not occur naturally in sufficient quantities.

Tritium is radioactive (a beta emitter), with a half-life of 12.3 years. It is also toxic.

Complete fusion reactions produce no long-life products. Induced radioactivity is produced in the reactor container due to neutron flux. Also, tritium is radioactive and quite toxic.

Sustaining a fusion reaction may be possible by containing the reactants in a high temperature form of matter called plasma. Plasma particles can be contained within a magnetic field. This principle is referred to as magnetic confinement. The purpose of magnetic confinement is to avoid heat loss, not to prevent the walls of the confinement vessel from vaporizing, as often believed.

Another possible technique for sustaining a fusion reaction is inertial confinement, in which a fuel pellet containing the fusion reactants is bombarded by a high energy source such as a laser or an electron beam.

The fusion bomb, developed and first exploded in the early 1950's, was the first use of nuclear fusion.

Learning Outcomes

Students will increase their abilities to:

1. Define the following terms: fusion, thermonuclear, plasma, magnetic confinement, inertial confinement.

2. Describe what happens during a fission reaction.

3. Explain that nuclear fusion occurs within the sun and the stars .

4. Recognize that scientists believe that nuclear fusion is possible under extremely high temperatures.

5. State that fusion reactions produce no long-term waste products.

6. Recognize that the fuel needed for a fusion reaction is abundant.

7. Compare fusion and fission.

8. Explain one possible way of sustaining a fusion reaction.

9. Suggest the potential that fusion has for providing an abundant supply of energy.