PRODUCTION OF PHOTOFISSION FRAGMENTS AND STUDY OF THEIR NUCLEAR STRUCTURE

摘要

Fission fragments of heavy nuclei (Z > 90) are neutron-rich isotopes of the elements from Zn (Z = 30) to Nd (Z = 60) with a neutron number of 45 - 90. The large neutron excess in the fission fragments under study (in some cases there are 10 - 15 more neutrons, than in the nuclei situated in the β-stability valley) could lead to an essential change in their structure and radioactive decay characteristics. The abnormal ratio of protons and neutrons in such nuclei reflects on spin-orbit interactions and can lead to another order of nucleon shell filling. This change will manifest itself in the appearance of new magic numbers of protons or neutrons, new regions of deformation, of new islands of isomerism. A striking example of such phenomena is found in light neutron-rich nuclei of ~(31)Na and ~(32)Mg at the magic number N = 20. Contrary to our knowledge about nuclear structure, these nuclei are strongly deformed. The same situation could occur in the case of very neutron-rich isotopes of Cu and Zn near N = 50 as well as Ag and Cd near N = 82. The high energy of β-decay can result in the appearance of new, much rare, modes of radioactive decay. They are emission of a neutron pair or an α-particle after β-decay (β2n or βα). These decay modes are an important source of new information about nuclear structure.