PRODUCTION OF PHOTOFISSION FRAGMENTS AND STUDY OF THEIR NUCLEAR STRUCTURE BY LASER SPECTROSCOPY

Thession fragments of heavy nuclei ( Z> 90) are neutron-rich isotopes of the elements from Zn (Z =3 0 )t o Nd (Z =6 0) with a neutron number of 50A95. The large neutron excess in thession fragments under study (in some cases there are 10A15 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 reects on spin- orbit interactions and can lead to another order of nucleon shelllling. This change will manifest itself in the appearance of new magic numbers of protons or neutrons, new regions of deformation and new islands of isomerism. A striking example of this phenomena has already been observed at the shell closure N =2 0in the light neutron-rich nuclei of 31 Na and 32 Mg. In contrast to our knowledge about nuclear structure,