Making an atomic bomb "A" requires: - Dispose of a neutron source , for example neutrons produced by bombardment of beryllium nuclei by alpha particles produced by a radioactive source. - Know to slow down these neutrons by a moderator, for example by water. - Dispose of enriched uranium 80%. Natural uranium is essentially a mixture of two isotopes $_{92}^{238}U$ (99.28%) and $_{92}^{235}$U (0.72%). Difficult physical processes, such as centrifugation or gaseous diffusion, based on slightly different masses of the two isotopes, allow to separate and obtain a mixture containing 80% $_{92}^{235}U$ . - Build the bomb by the following scheme:
The fission reaction in a sub - critical mass does not produce enough neutrons to maintain the reaction. - Bring both sub - critical masses together through a conventional explosion. The number of neutrons will multiply exponentially as a result of the chain reaction and the bomb explodes, releasing suddenly the enormous energy of the fission.
