Nuclear Fission

             The atomic bomb (also known as the atom bomb, A-bomb , or nuclear bomb) has a destructive power created by the fission of either uranium or plutonium.  But, not any isotope of uranium can be used.  Only U235 is used in the production of an atom bomb.  U235 is very hard to come by due to the fact that it is only present within 0.7% of all natural uranium.  In order to separate the U235 isotope from natural uranium a process of enrichment is used.  The uranium must be enriched to 90% for actual use in a bomb. 
                                     

  The Enrichment Process

                      The enrichment process is complicated due to the fact that the uranium isotopes are practically chemically identical.  This means that the different isotopes cannot be separated with just an easy chemical reaction.  The isotopes must be separated by exploiting the little mass difference between the isotopes.  There are many different methods used to separate these isotopes a couple of these are the commercial-gaseous diffusion process and the centrifuge process.  Another method of separation is the Electro Magnetic Separation process.
   
*Electro Magnetic Separation*
  
                           
                            This enrichment method was created by E.O. Lawrence.  It involves passing uranium ions through a magnetic field
which causes the U235 ions to separate and take a different path than the U238 ions.  Following this collectors are used at the other end of the semi-circle to capture the separated U235.           

    Fission of U235                                              

                  Fission is when a nucleus splits into many small fragments called fission products.  These fission products become nearly half the mass of the original nucleus and the nuclues generally emits two to three neutrons.



www.atomicarchive.com/Fission/Fission1.shtml


                                                    U235 and  Plutonium each have the inherent ability to fission making them perfect candidates for the atomic bomb.  Plutonium 239 has a very high spontaneous fission rate making it easy to for the bomb to accidently fizzle before production is complete.  While Uranium 235 has a lower rate of spontaneous fission making it easier to deal with when building an atom bomb.