Fission and Fusion
4 marks · EasyNuclear reactions release energy in different ways. Uranium-235 is used as a fuel in some nuclear power stations, while nuclear fusion occurs in stars.
Explain what happens when a nucleus of uranium-235 absorbs a slow-moving neutron.
State what nuclear fusion involves and where it naturally occurs.
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(a) The uranium-235 nucleus absorbs the neutron, becoming uranium-236, which is unstable. It then splits (fissions) into two lighter (radioactive) nuclei, releasing energy and a few neutrons. · must show absorption of neutron, unstable intermediate nucleus, splitting into two lighter nuclei, release of energy and neutrons
(b) Nuclear fusion is when two light nuclei join to make a heavier nucleus and energy is released; fusion occurs naturally in stars (e.g., the Sun). · must show joining of light nuclei, release of energy, occurs in stars
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Marking points
M1 (a) · 1 mark · Explains absorption of neutron and formation of unstable nucleus.
A1 (a) · 1 mark · States splitting produces lighter nuclei, energy, and neutrons.
M2 (b) · 1 mark · States that fusion is the joining of two light nuclei to form a heavier nucleus with release of energy.
A2 (b) · 1 mark · States that fusion occurs in stars (such as the Sun).
Worked solution
a) When a uranium-235 nucleus absorbs a slow-moving neutron, it becomes uranium-236 which is unstable. This unstable nucleus splits into two lighter nuclei (fission fragments), releasing energy and additional neutrons.
b) Nuclear fusion is when two small (light) nuclei join together to form a larger nucleus with a release of energy. Fusion occurs naturally in stars, such as the Sun.