Chain Reactions (AQA GCSE Physics): Revision Notes
📚 Revision Notes
4.4.2 Chain Reactions
infoNote
Neutrons can start a chain reaction. The neutrons released from a fission reaction will have kinetic energy. Therefore, the neutrons can move around and become absorbed by another large, unstable nucleus. This will lead to a second fission reaction, resulting in a chain reaction.
Controlling the Chain Reaction
- Chain reactions can be dangerous. It is very difficult to stop a chain reaction, meaning it can become dangerous very quickly. Many neutrons are produced by each fission reaction, leading to multiple fission reactions.
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Nuclear reactors use control rods. Inside a nuclear reactor, there is a controlled series of fission reactions occurring. We do this by using control rods inside the reactor.
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Control rods absorb neutrons. By placing control rods into the reactor, we can absorb excess neutrons. We know that neutrons induce fission reactions, so by absorbing some of them, we are limiting the number of fission reactions that occur.
- Nuclear weapons have uncontrolled reactions. Inside a nuclear weapon, there are uncontrolled nuclear fission reactions happening. This means that there is an uncontrolled chain reaction, which ultimately leads to an explosion.