Fission and fusion for SQA Higher Physics
This page covers the following topics:
3. Induced fission
Fission is the process by which a large atomic nucleus is split up into smaller nuclei. A neutron hits a nucleus and is absorbed by it. This causes the nucleus to become unstable and thus it splits up into smaller nuclei, called the daughter nuclei, and more neutrons. The neutrons released carry most of the energy of the fission reaction as kinetic energy, and thus have to be slowed down before colliding with other nuclei. Fission has an advantage in generating energy over fossil fuels due to the fact that it requires less fissionable material to produce the same amount of energy.
Nuclear fusion is the process by which small and light nuclei join together to form a bigger and heavier nucleus. Comparing the combined mass of the smaller nuclei to the mass of the resulting nucleus may show that the latter is smaller. This missing mass is converted into energy and is radiated away. Fusion reactions must be quick to occur, so that the repulsion between the two positively charged nuclei does not have time to act. Nuclear fusion must also occur in very high temperatures and pressures to overcome the repulsion between the nuclei.
Induced fission occurs by firing neutrons into a nucleus to cause fission. During this fission process, more neutrons are released from the nucleus. These neutrons in turn hit other nuclei and thus a chain reaction of fission processes is formed. This chain reaction will go on until all the available material has undergone fission. Moderators are used in induced fission. Control rods are also used in induced fission to control the reaction by absorbing neutrons. These rods may be inserted or removed from the reactor whenever necessary. A coolant is used in induced fission to stop the reactor from combusting.
Why are coolants used in induced fission reactors?
Coolants are placed inside the reactor to prevent it from combusting.
Define nuclear fusion.
Nuclear fusion is the process by which two small and light nuclei join together to form a bigger and heavier nucleus.
How does absorbing a neutron cause a nucleus to split?
Absorbing a neutron makes the nucleus unstable, which causes it to split.
Draw a diagram to represent nuclear fission.
What happens to the energy of a nuclear fission reaction?
The energy of the fission reaction is transferred to kinetic energy in the neutrons formed by the reaction.
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