Nuclear Fission
Physics: IB Diploma Higher Level, topic 5.2.2
Fission
Nuclear fission is a reaction in which a nucleus is split (or fissured).
Fission
- Energy is released when heavy nuclei are split apart.
- The new nuclei (daughter nuclei) have a larger binding energy per nucleon than the parent.
- This means that a large amount of energy is released (about 100 times the energy of a normal nuclear decay).
Chain reaction
- Fission occurs when an unstable atom splits, we can force this split by making the atom absorb a neutron.
- The fission reaction will produce daughter nuclei but also release energy and some neutrons.
- These neutrons will go on to cause fission reactions themselves, which will produce more neutrons.
- This is now a chain reaction.
Fusion
Nuclear fusion is a reaction in which two nuclei are combined, or fused, to form a larger nucleus.
Fusion
- We know that all nuclei have less mass than the sum of the masses of the protons and neutrons.
- When an atom is formed it releases binding energy - the greater the binding energy, the greater the missing mass.
- The binding energy per nucleon is a maximum at iron.
- This means that if two low-mass nuclei can be fused together to form a larger nucleus, energy can be released.
Making fusion work
- Fusion would release a huge amount of energy but there are many issues that need to be overcome before it will work on earth.
- The repulsion between positive nuclei is very strong and can only be overcome at very high temperatures or pressures.
Energy from fusion
- We can use the energy and mass equation:
- If we know the mass of the nuclei before and the mass of the large nucleus afterward we can find the change in mass.
- If we know the change in mass we can find the energy released.
Test yourself on Nuclear Fission
When neutrons are produced in fission they cause more fission reactions, what is this called?
Binding energy per nucleon is highest at which element?
How can we find the energy released in fusion?