The New-Revealed Regularities of Fragment Mass Yields from the Proton Induced Fission of Actinide Nuclei

The mass and energy distributions of fragments from the proton induced fission of compound nuclei ^234,237,239Np, ^{239,240,241,243}Am, ²⁴⁵Bk at proton energy E_p = 10.3 MeV, ²³³Pa, and ²³⁶Np at E_p = 7.4 - 30.0 MeV have been measured and analyzed in terms of the multi-modal fission on the basis of a new-developed method for the multi-modal deconvolution that is free from any parametrization of the distinct fission mode mass distribution shapes. At excitation energies above 10 MeV the strong correlations have been revealed in the behaviour of the characteristics of two predominant asymmetric modes Standard 1 and Standard 2. This effect could be interpreted as an indication of that mode Standard 2 is mainly formed under the influence of spherical shell closures Z = 50 and N = 82, as well as Standard 1, and several nucleons attached from the neck. The characteristics of the asymmetric fission mass distributions are shown to be mainly defined by the proton numbers of compound actinide nuclei and demonstrate only weak dependence on the neutron ones. At this, the sharply expressed grouping of the asymmetric fission mass yields at Z ≤ 51 in heavy fragments and at Z ≤ 31 in light ones has been observed.