Successive neutron captures
Multiple captures of neutrons are responsible for the formation of plutonium isotopes and actinides in reactors. This map of nuclei shows how a succession of neutron captures and beta decays generates the isotopes of plutonium. In the case of plutonium-239 and plutonium-241, considerd fissile, the capture of slow neutrons triggers often a fission. Fast neutrons are able to split the other isotopes of plutonium.