Why neutron moderation is needed? x(E)=0.453ex(-1.036E)sinh(2.29E)0 10 0 leutron energy(Mev) Fission neutron energy spectrum The average energy of prompt fission neutrons is about 2 MeVFission neutron energy spectrum Why neutron moderation is needed? The average energy of prompt fission neutrons is about 2 MeV