The splitting of heavy nuclei into lighter fragments, releasing energy.
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Explain how Uranium 235 has a fission reaction
U-235 is hit by a slow neutron, this causes it to become U-236 which is unstable. It then breaks apart, giving out energy.
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What are the products of fission reactions?
Lots of energy, a number of new (daughter nuclei) that may be radioactive with range of half lives and, a number of neutrons- which can go on to cause other fission reactions.
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What is spontaneous fission?
When fission occurs without a neutron being captured by the atom.
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What is stimulated fission?
When fission occurs without a neutron being captured by the atom.
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What is a chain reaction?
A fission reaction emits neutrons which causes another reaction, which then produces more neutrons that will cause another fission reaction... etc.
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What is critical mass?
For a chain reaction to occur, the mass needs to be large enough. This mass is known as the critical mass.
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How does a nuclear reactor produce electricity?
A nuclear fission reaction is used to heat water, that produces steam that will then turn a turbine.
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How are fission reactions controlled?
Moderators and control rods are used to speed (increase energy output) and slow down (decrease energy output).
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What is a moderator?
They slow down the neutrons which causes them to be captured easier by the uranium. This causes more reactions to occur (more energy released).
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What is a control rod?
Used to capture neutrons and reduce number available for reactions to take place. This reduces the amount (less energy) and can prevent chain reactions from becoming an explosion.
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What are the advantages of fission?
They give off a large amount of energy and they do not produce any pollutant gases.
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What are the disadvantages of fission?
Produces radioactive waste that has to be stored for 1000s of years, until it is safe. Also there's a risk of explosion.
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What is fusion?
E.g. 2H+3H=5H=4H+n. When light nuclei collide at high speeds, they come together to form a larger nuclei/
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What is the most important fusion reaction to us?
When hydrogen fuses to make helium. This is important because it occurs in the sun.
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What are the advantages of fusion?
Clean energy source, doesn't give out anything harmful. Produces huge amounts of energy and can use hydrogen taken from sea, to react - we have lots of it.
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What are the disadvantages of fusion?
Large amount of energy. The only way to produce the energy needed to start a fusion reaction, would be to use fission. The fusion reaction would be so hot that nothing on earth would be able to hold it. Impossible to stop.
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What problems do we face with shielding of radiation?
Gamma- Can cause cancer. Neutron radiation- fission/fusion give out neutrons, if they are abosorbed by any material (inc. skin), it will cause the nuclei to undergo fission- very bad.
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What can we do to shield with fission and fusion reactions?
Gamma- lead and concrete. Neutron- concrete combined with water and hydrocarbons are used, that can absorb neutrons safely.
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Other cards in this set
Card 2
Front
Explain how Uranium 235 has a fission reaction
Back
U-235 is hit by a slow neutron, this causes it to become U-236 which is unstable. It then breaks apart, giving out energy.
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