A new statistical method for systematizing the nuclei fission fragments, investigation of their mass and charge spectra and neutron fission parameters has been suggested. In proposed method, the mass and charge yields of nucleons are determined from the equilibrium conditions of the nuclear fragments post-fission ensemble. Here we consider protons and neutrons of different fragments as statistically non-equivalent. The abilities of the proposed statistical method for explanation of the U, Pa, Th, Ac and Ra post-fission fragments ordering and neutron emission function calculation have been demonstrated.

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The first results about the features of the fission fragments yields and spectrum of the energy of fission over 100 isotopes of uranium are presented. The role of neutrons shells with N = 82 or N = 126 and protons shells with Z = 50 in the realization of symmetric (or onehumped) and asymmetric (2-or 3-humped) shapes of the fission fragment yields was investigated. It was shown that studies of Kr isotope yields under fission of uranium isotopes give also valuable information on the role of the mentioned nuclear shells, too. The obtained results can be useful in similar studies of other actinide nuclei.

The "many ensembles" method was proposed to investigate the influence of nuclear particles' post-scission emission on mass and charge distributions of fission products. The post scission approximation had been used; each of these ensembles consists of the fission fragments after emission of chains of different lengths, both the beta (±β) particles and neutrons. The theory allows one to find the most probable two fragment clusters of fission products and study their evolution after the post-scission emission of nuclear particles. The isotope ²³²Th was chosen as an example, the fission fragments of which are intensively studied in the experiment. It is shown that the post-scission emission of nuclear particles eventually leads to the convergence of the asymmetric peaks, which looks like enhanced symmetric fission mode over asymmetric one for fission product yields. A comparison of the theoretical results and experimental data for the ²³²Th fission fragments indicates their satisfactory matching.