Synthesis and decay properties of the heaviest nuclei

The formation and decay properties of the heaviest nuclei with Z = 112-116 and 118 were studied in the reactions U-238, Pu-242,Pu-244, Am-243, Cm-245,Cm-248 and Cf-249 + Ca-48. The new nuclides mainly undergo sequential alpha-decay, which ends with spontaneous fission. The total time of decay ranges from 0.5 ms to similar to 1 day, depending on the proton and neutron numbers in the synthesized nuclei. The atomic number of the new elements 115 and 113 was confirmed also by an independent radiochemical experiment based on the identification of the neutron-rich isotope (268)Db (T-SF similar to 30 h), the final product in the chain of alpha-decays of the odd-odd parent nucleus (288)115. The comparison of the decay properties of 29 new nuclides with Z = 104-118 and N = 162-177 gives evidence of the decisive influence of the structure of superheavy elements on their stability with respect to different modes of radioactive decay. The investigations connected with the search for superheavy elements in Nature and prospects of superheavy element research are also presented. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions (JINR, Dubna) in collaboration with the Analytical and Nuclear Chemistry Division of the Lawrence Livermore National Laboratory (USA).