|Formation of isotopes 236, 233 and 232|
The isotopes 236, 233 and 232 of uranium are formed in reactors from captures of neutrons not followed by fission. Uranium-236 is formed by a simple radiative capture by a nucleus of uranium-235 in contrast with captures that cause fission. Uranium-233 is formed by a similar capture by a nucleus of natural thorium, followed by two radioactive transformations. Uranium 233 is fissile itself. Submitted to the flow of neutrons from a reactor, it undergoes fission, but more rarely turns into uranium 232 by a reaction of specific capture (n, 2n) that triggers the expulsion of two neutrons.