Natural uranium contains the common isotope 238 U and the uncommon isotope 235U. The principal mecha- nism of fission of natural uranium isotopes, 238U and 235U, is neutron capture with the formation of compound nuclei 23ºU and 236U in excited state. The neutron binding energies in 239U and 236U are 5.5 and 6.8 MeV, respectively. The fission barrier heights are 7.1 and 6.5 MeV for 239U and 236U, respectively. Discuss what happens when 235U and 235U are exposed to slow (thermal) neutrons (with kinetic energies less than 0.5 keV) or fast neutrons (with kinetic energies on the order of 2 MeV).

Natural uranium contains the common isotope 238 U and the uncommon isotope 235U. The principal mecha- nism of fission of natural uranium isotopes, 238U and 235U, is neutron capture with the formation of compound nuclei 23ºU and 236U in excited state. The neutron binding energies in 239U and 236U are 5.5 and 6.8 MeV, respectively. The fission barrier heights are 7.1 and 6.5 MeV for 239U and 236U, respectively. Discuss what happens when 235U and 235U are exposed to slow (thermal) neutrons (with kinetic energies less than 0.5 keV) or fast neutrons (with kinetic energies on the order of 2 MeV).