Nuclear fusion and fission

Nature of science:

Assessing the ethics of scientific research—widespread use of nuclear fission for energy production would lead to a reduction in greenhouse gas emissions. Nuclear fission is the process taking place in the atomic bomb and nuclear fusion that in the hydrogen bomb. (4.5)

Understandings:

Nuclear fusion

• Light nuclei can undergo fusion reactions as this increases the binding energy per nucleon.
• Fusion reactions are a promising energy source as the fuel is inexpensive and abundant, and no radioactive waste is produced.
• Absorption spectra are used to analyse the composition of stars.

Nuclear fission

• Heavy nuclei can undergo fission reactions as this increases the binding energy per nucleon.
• ²³⁵U undergoes a fission chain reaction:               neutrons.
• The critical mass is the mass of fuel needed for the reaction to be self- sustaining.
• 239Pu, used as a fuel in “breeder reactors”, is produced from 238U by neutron capture.
• Radioactive waste may contain isotopes with long and short half-lives.
• Half-life is the time it takes for half the number of atoms to decay.

• The use of nuclear energy is monitored internationally by the International Atomic Energy Agency.
• High-energy particle physics research involves international collaboration. There are accelerator facilities at CERN, DESY, SLAC, Fermi lab and Brookhaven. Results are disseminated and shared by scientists in many countries.
• The ITER project is a collaboration between many countries and aims to demonstrate that fusion is an energy source of the future.

Theory of knowledge:

• The use of nuclear energy carries risks as well as benefits. Who should ultimately be responsible for assessing these? How do we know what is best for society and the individual?

Utilization:
Syllabus and cross-curricular links:
Topic 2.1—isotopes
Topic 2.2—the emission spectrum of hydrogen
Physics topic 7.2—nuclear fusion

Aims:

• Aim 7: Computer animations and simulations of radioactive decay, and nuclear fusion and fission reactions.
• Aim 8: Consideration of the environmental impact of nuclear energy illustrating the implications of using science and technology.

Applications and skills:

Nuclear fusion

• Construction of nuclear equations for fusion reactions.
• Explanation of fusion reactions in terms of binding energy per nucleon.
• Explanation of the atomic absorption spectra of hydrogen and helium, including the relationships between the lines and electron transitions.

Nuclear fission

• Deduction of nuclear equations for fission reactions.
• Explanation of fission reactions in terms of binding energy per nucleon.
• Discussion of the storage and disposal of nuclear waste.
• Solution of radioactive decay problems involving integral numbers of half-lives.

Guidance:

• Students are not expected to recall specific fission reactions.
• The workings of a nuclear power plant are not required.
• Safety and risk issues include: health, problems associated with nuclear waste and core meltdown, and the possibility that nuclear fuels may be used in nuclear weapons.
• The equations,  are given in section 1 of the data booklet.