The uranium-238, uranium-234, and uranium-232 are fertile material.
The most common isotopes in natural uranium are uranium-238 (which has 146 neutrons and accounts for over 99% of uranium on Earth) and uranium-235 (which has 143 neutrons). In nature, uranium is found as uranium-238 (99.273999.2752%), uranium-235 (0.71980.7202%), and a very small amount of uranium-234 (0.00500.0059%). Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Uranium-234 (U, U-234) is an isotope of uranium. In natural uranium and in uranium ore, U occurs as an indirect decay product of uranium-238, but it makes up only 0.0055% (55 parts per million) of the raw uranium because its half-life of just 245,500 years is only about 1/18,000 as long as that of U.  U  is also formed in this process, via (n,2n) reactions between fast neutrons and U ,  Pa , and Th : U has a relatively short half-life (68.9 years), and some decay products emit high energy gamma radiation, such as  Rn ,  Bi  and particularly  Tl . The full decay chain, along with half-lives and relevant gamma energies, is: U decays to  Th  where it joins the decay chain of Th  Fertile material is a material that, although not itself fissionable by thermal neutrons, can be converted into a fissile material by neutron absorption and subsequent nuclei conversions. Naturally occurring fertile materials that can be converted into a fissile material by irradiation in a reactor include: uranium-238 which converts into plutonium-239 uranium-234 which converts into uranium-235 
