Nuclear Fission

Key Stage 4

Meaning

An model of nuclear fission.

Nuclear fission is a process in which a large unstable nucleus splits into two more stable nuclei.

About Nuclear Fission

Nuclear fission occurs when a massive nucleus is so unstable that it splits in two.

During nuclear fission neutrons are also emitted.

Nuclear fission transfers energy from the nuclear potential energy store into the thermal energy store of the material and the surroundings.

In a nuclear fission reaction the products have less mass than the reactants as some of the mass is converted into energy in the process due to the Mass-Energy Equivalence.

Nuclear fission can be induced in a material by bombarding massive nuclei with neutrons. If a neutron is captured by the nucleus it becomes so unstable that it splits in two.

The neutrons used to induce fission must have a low energy to be captured by a nucleus otherwise the neutrons will just pass straight through without being captured. Neutrons with the right amount of energy to be captured are called thermal neutrons because they have a similar energy to molecules in the air at room temperature.

A model showing a possible mechanism for induced nuclear fission resulting from the capture of a thermal neutron. \({}_{92}^{235}U + {}_{0}^{1}n \rightarrow {}_{92}^{236}U \rightarrow {}_{36}^{85}Kr + {}_{56}^{148}Ba + 3{}_{0}^{1}n\)

If there is enough of an unstable isotope in a material a single nuclear fission can trigger a nuclear chain reaction in which the neutrons produced from the initial fission event can cause the fission of more than one other unstable isotope.

A nuclear fission chain reaction is used in both nuclear bombs and nuclear reactors in nuclear power stations.

References

AQA

Nuclear fission, page 140, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA

Nuclear fission, page 49, GCSE Physics; The Revision Guide, CGP, AQA

Nuclear fission, pages 104-105, GCSE Physics; Third Edition, Oxford University Press, AQA\

Nuclear fission, pages 106-7, GCSE Physics, Hodder, AQA

Edexcel

Nuclear fission, page 166, GCSE Combined Science, Pearson Edexcel

Nuclear fission, page 22, GCSE Chemistry, Pearson, Edexcel

Nuclear fission, page 57, GCSE Physics; The Revision Guide, CGP, Edexcel

Nuclear fission, pages 110, 112-113, GCSE Physics, Pearson Edexcel

Nuclear fission; power generation, page 113, GCSE Physics, Pearson Edexcel