- It is rare for nuclei to undergo fission without additional energy being put into the nucleus
- When nuclear fission occurs in this way it is called spontaneous fission
- Usually, for fission to occur the unstable nucleus must first absorb a neutron
- This makes the nuclei more unstable, so that it decays almost immediately
Fission of Uranium-235
- Uranium-235 is commonly used as a fuel in nuclear reactors
- It has a very long half-life of 700 million years
- This means that it would have a low activity and energy would be released very slowly
- This is unsuitable for producing energy in a nuclear power station
- During induced fission, a neutron is absorbed by the uranium-235 nucleus to make uranium-236
- This is very unstable and splits by nuclear fission almost immediately