Fission barrier of superheavy nuclei and persistence of shell effects at high spin: cases of 254No and 220Th

Synthesis and properties of isotopes of the transactinides

Isotopes of transactinide elements have to be synthesized in nuclear reactions with light or heavy beam particles. The efficient production by neutron capture and subsequent β − decay as it is used for the production of isotopes of actinide elements up to fermium is no longer possible due to the lack of suitable target material. The content of this article is about the synthesis and the study of the decay properties of nuclei to which atomic, respectively proton numbers from Z = 104 to 118 could be unambiguously assigned by physical means. The results identified the reaction products as isotopes of new elements beyond the actinides, the transactinides. As such the elements received names given by the discovers ranging from rutherfordium for element 104 to oganesson for element 118 which completes the 7th row of the Periodic Table of the Elements. Intensive heavy ion beams, sophisticated target technology, efficient electromagnetic ion separators, and sensitive detector arrays were the prerequisites for discovery of the elements from Z = 107 to 118 during the years from 1981 to 2013. The results and the techniques are described. Also given is a historical introduction into early experiments and the theoretical predictions for a possible existence of an island of stability located at the crossing of the next closed shells for the protons and neutrons beyond the doubly magic nucleus 208Pb. The experimental results are compared with recent theoretical calculations on cross-sections and decay modes of these superheavy nuclei, respectively isotopes of superheavy elements. An outlook is given on further improvement of experimental facilities which will be needed for exploration of the extension and structure of the island of superheavy nuclei, in particular for searching for isotopes with longer half-lives predicted to be located in the south east and for isotopes of further new elements expected in the north-east direction of the island at the upper end of the chart of nuclei.