Neutron capture can also induce radioactivity through activation. The capture of a neutron excites the nucleus, which quickly decays to a less energetic state through the emission of radiation. Some activation reactions and products of significance in power reactors include the following:
Cobalt-60 and iron-55 are common activation products in the structural components of reactors.
The isotopes produced by these neutron capture processes are almost always radioactive. Their decay involves the emission of alpha, beta, and gamma radiation, to produce both radioactive and nonradioactive decay products. A decay reaction of particular importance in nuclear power reactors is the following:
This reaction produces plutonium-239 by uranium-238 neutron capture followed by two beta decays.
The particles and other radiation emitted during neutron capture can interact with atoms in the fuel, coolant, and reactor structures to produce additional radioactivity. For example, the interaction of energetic electrons with materials in the reactor results in the emission of photons known as bremsstrahlung. This radiation appears as a faint blue glow when electrons interact with cooling water in the reactor and spent fuel pools.