Term
| What is nuclear fusion and how can it occur? |
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Definition
Nuclear fusion is the merging of small nuclei to make a larger nucleus. It can occur because the resulting nucleus has less binding energy per nucleon than it did when they were smaller nuclei, making it more stable. This results in a loss of energy, and therefore loss of mass according to ΔE = Δmc2 |
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Term
| What must nuclei overcome in order to fuse? |
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Definition
Work must be done to overcome the electrostatic (Coulomb) force of repulsion For this to happen, the nuclei must have enough kinetic energy to overcome the 'Coulomb barrier' and become close enough to each other for the strong force to act between them
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Term
| What equation can be used to find the temperature needed for fusion? |
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Definition
Ek = 3 kT 2 k = Boltzmann constant, 1.38x10-23 JK-1 |
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Term
| What fusion reactions occur in stars e.g. The Sun? |
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Definition
| The carbon cycle and the hydrogen cycle |
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Term
| Explain the hydrogen (proton-proton) cycle |
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Definition
2 protons fuse, producing a hydrogen-2 (deuterium) nucleus, a positron and a neutrino A hydrogen-2 nucleus and a proton fuse, and this produces a helium-3 nucleus and some gamma radiation 2 helium-3 nuclei fuse together making a helium-4 nucleus, 2 protons and some gamma radiation The 2 protons fuse... etc
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Term
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Definition
Carbon-12 fuses with a proton, making nitrogen-13 and gamma radiation This turns into carbon-13, emitting a positron and neutrino The carbon-13 fuses with a proton, producing nitrogen-14 and gamma radiation This fuses with a proton making oxygen-15 and gamma radiation This oxygen-15 turns into nitrogen-15, emitting a positron and neutrino The nitrogen-15 fuses with a proton, producing a helium-4 nucleus and carbon-12 The carbon-12 fuses with a proton... etc
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Term
| Why is the Sun considered as a nuclear fusion reactor? |
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Definition
| Its great mass produces a large gravitational force, resulting in a very high core temperature, so lots of hydrogen cycles can occur. Even though the rate of reaction is quite low, the Sun has so many protons that the overall rate of reaction is high. |
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Term
| What is the most practical and favoured reaction for a fusion reactor on Earth? |
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Definition
Deuterium-tritium (D-T) fusion Single stage fusion reaction Relatively low Coulomb barrier Releases more energy per fusion Gives a net energy gain at a lower temperature
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Term
| What are the problems with having nuclear fusion as an energy source on Earth? |
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Definition
Small nuclei used need to be at very high temperatures, making a mixture of positive ions and electrons known as plasma It is hard confining the hot plasma so it retains its energy and doesn't melt the material the reactor is made from In the Sun gravitaional forces confine the plasma, on Earth strong magnetic fields or inertial confinement is used (heat and compressing the fuel quickly)
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