What are the two most common fissionable substances used in nuclear reactors?
Uranium-235 and plutonium-239
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What must happen for fission to occur in uranium-235 and plutonium-239?
The nucleus must absorb a neutron
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What then happens in the process of fission in uranium-235 and plutonium-239?
The nucleus splits into two smaller nuclei, releasing two or three neutrons which can go on to cause further fission, and energy is released in great qantites
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When does a chain reaction occur?
When each fission event causes further fission events
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In a nuclear fission reactor, how are chain reactions controlled?
By control rods which absorb the neutrons. The rods ensure that, on average, only one neutron per fission goes on to produce further fission. In this way, energy is released at a steady rate.
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What is nuclear fusion?
The process of forcing two nuclei close enough together so the form a single larger nucleus
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How can nuclear fusion be brought about?
By making two light nuclei collide at very high speed
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How is energy released in stars?
By nuclear fusion in the nuclei
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How long ago was the universe created?
13 billion years ago
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How are stars formed?
When dust and gas are pulled together by gravitational attraction. The resulting intense heat starts nuclear fusion reactions so they begin to emit visible light
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What are galaxies?
Large groups of stars
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Gravitational forces pull clouds of dust and gas together to form what?
A protostar
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What happens when the protostar gets denser?
The nuclei of hydrogen atoms and other light elements start to fuse together and energy is released in the process so the core gets hotter and brighter
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Why are main sequence stars stable?
Because the inward force of gravity is balanced by the outward force of radiation
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What happens when a star runs out of hydrogen nuclei?
It swells, cools down and turns red. Helium and other light elements fuse in its core to form heavier elements
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What is the life cycle of a low mass star, like the Sun?
Protostar, main sequence star, red giant, white dwarf, black dwarf
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What is the life cycle of a high mass star?
Protostar, main sequence star, red supergiant, supernova and either a neutron star, or if it is big enough, a black hole
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How are nuclei larger than iron formed?
In the collapse of a high mass star (supernova). This is because the fusion process requires the input of energy
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Other cards in this set
Card 2
Front
What are the two most common fissionable substances used in nuclear reactors?
Back
Uranium-235 and plutonium-239
Card 3
Front
What must happen for fission to occur in uranium-235 and plutonium-239?
Back
Card 4
Front
What then happens in the process of fission in uranium-235 and plutonium-239?
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