Neutron Emission from Fission Modes

The number and energy of neutrons and the average energy of prompt gamma rays emitted from various fission modes are estimated from the excitation-energy distributions of fragments from these modes. These excitation-energy distributions are derived from the mass equation of fission and the measured kinetic energies of the fragments. Simple considerations of neutron boil-off are used with these excitations.For the most probable mass ratios of fragments, the variation in the average number of neutrons ν with the total kinetic energy EK of the fragments is found to be dνdEK=-0.121 Mev^-1 for thermal-neutron fission of U²³⁵ and -0.116 Mev^-1 for spontaneous fission of Cf²⁵². The spectra of neutron energies resulting from this analysis are found to have negligible change with EK, but the neutrons from Cf²⁵² fission are more energetic than those from thermal-neutron fission of U²³⁵. The average energy E_γ of prompt gamma rays from Cf²⁵² fission is found to be 4.0 Mev, with a variation dE_γdEK=-0.0167 for the most probable mass ratios of fragments.