Nuclear Fission & Fusion (AQA GCSE Physics): Flashcards
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Define nuclear fission.
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Define nuclear fission.
Nuclear fission is the splitting of a large, unstable nucleus into two smaller nuclei.
Which two elements' isotopes undergo fission and are used as fuels in nuclear power stations?
Uranium and plutonium.
When a neutron collides with an unstable nucleus and it splits by fission, what is released in addition to two smaller daughter nuclei?
Two or three neutrons are released, along with gamma rays.
During fission, energy is transferred from nuclear potential energy to ______ energy.
During fission, energy is transferred from nuclear potential energy to kinetic energy.
Define spontaneous fission.
Spontaneous fission is when nuclear fission occurs without additional energy being put into the nucleus. It is rare.
True or False?
Uranium-235 has a low activity and a long half-life, so it can release energy quickly enough to be used directly as a nuclear power station fuel.
False.
Uranium-235 has a very long half-life and low activity, so it releases energy too slowly to be used directly. It must first absorb a neutron before it can undergo fission at a usable rate.
What happens when a uranium-235 nucleus absorbs a neutron during induced fission?
It forms a more unstable nucleus, which splits by nuclear fission almost immediately.
Define chain reaction.
A chain reaction is a process in which the neutrons released by each fission reaction go on to start further fission reactions, creating more excess neutrons each time.
How many extra neutrons are needed to induce a uranium-235 nucleus to split by fission?
Only one extra neutron.
How many neutrons are produced during a single fission reaction, and how do they move?
Two or three neutrons are produced, and they move away at high speed.
Define control rods.
Control rods are rods in a nuclear reactor that absorb neutrons without becoming dangerously unstable themselves.
In a nuclear reactor, the number of free neutrons must be kept ______ for the reactor to produce energy at the correct rate.
In a nuclear reactor, the number of free neutrons must be kept constant for the reactor to produce energy at the correct rate.
True or False?
A nuclear weapon uses a controlled chain reaction to release energy gradually.
False.
A nuclear weapon uses an uncontrolled chain reaction, in which the number of neutrons and reactions increases quickly, releasing a huge amount of energy in a short period of time as an explosion.
What is fired into a target nucleus to start a nuclear fission reaction, as shown in fission diagrams?
A neutron, which causes the target nucleus to split.
Why are diagrams useful for showing the processes involved in nuclear fission?
They show clearly the different parts of the fission reaction, in a way that is easy to understand.
When drawing a chain reaction diagram, which particles need to be shown?
Only the neutrons and uranium-235 nuclei need to be shown; the daughter nuclei do not need to be shown.
When drawing a chain reaction diagram, what must be shown once a uranium-235 nucleus splits?
That the splitting produces two or more neutrons.
Each fission reaction in a chain reaction requires one neutron but releases ______.
Each fission reaction in a chain reaction requires one neutron but releases two or three neutrons.
True or False?
In chain reaction diagrams, the number of neutrons decreases as more fission reactions occur.
False.
The number of neutrons increases with each fission reaction, so more reactions happen as the number of neutrons increases.
Define nuclear fusion.
Nuclear fusion is when two light nuclei join to form a heavier nucleus, releasing energy.
Where does nuclear fusion naturally take place?
In the centres of stars.
What is produced when hydrogen nuclei fuse together in stars?
Helium nuclei, releasing a large amount of energy.
Nuclear fusion requires extremely ______ temperatures to be maintained.
Nuclear fusion requires extremely high temperatures to be maintained.
Why does nuclear fusion require extremely high temperatures to occur?
Hydrogen nuclei are positively charged, so there is a repulsive force between them. High temperatures give the nuclei enough energy to overcome this repulsive force.
What equation describes the mass-energy equivalence in nuclear fusion?
E = m × c^2^, where E is the energy released (J), m is the mass converted into energy (kg), and c is the speed of light (m/s).
How much energy is released when 1 kg of hydrogen undergoes fusion, compared to burning coal?
It is equivalent to the energy released from burning about 10 million kilograms of coal.
True or False?
Hydrogen is a rare element, which is why fusion is commercially difficult to achieve on Earth.
False.
Hydrogen is the most common element in the universe, so it is abundant. The real challenge is achieving the extremely high temperatures needed for fusion to occur.
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