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 238 U, 242,244 Pu, 243 Am, 245,248 Cm and 249 Cf + 48 Ca. The new nuclides mainly undergo sequential α-decay, which ends with spontaneous fission. The total time of decay ranges from 0.5 ms 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 ∼30 h), the final product in the chain of α-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).