Key ideas1 of 3
Start with a large unstable nucleus
Nuclear fission is the splitting of a large, unstable atomic nucleus into two smaller nuclei. In induced fission, a neutron is absorbed by a suitable nucleus, such as uranium-235 or plutonium-239, making it unstable enough to split. Fission can also occur spontaneously in some nuclei. This is a nuclear change, not a chemical reaction that merely rearranges electrons or bonds between atoms.
