Statistical Theory of Nuclear Fission: Asymmetric Fission

A statistical theory is developed, according to which the relative probability of a mode of fission is determined by the total excitation energy of its two fragments calculated at the moment just before separation. In order to calculate the excitation energy, the well known semiempirical atomic mass formula is corrected for its deviations known to be attributed to the effects of nuclear shells. The nuclear level density expression is studied empirically with special attention to shell effects. These results are used for a quantitative calculation of the relative probabilities of all possible modes of fission. The mass distribution curve of fission products of U²³⁵ induced by thermal neutrons is derived and compared with experimental results. Applications of the statistical theory to charge distribution, kinetic energy distribution, variations of mass, charge and energy distributions with respect to target nucleus and incident energy, prompt neutron distribution, spontaneous fission yields, and ternary fission will be discussed briefly.