Synthesis and Decay Properties of Superheavy Nuclei

We have studied the dependence of the production cross sections of the isotopes ^282,283112 and ^286-288114 on the excitation energy of the compound nuclei ²⁸⁶112 and ²⁹⁰114. The maximum cross sections of the xn-evaporation channels for the reaction ²³⁸U(⁴⁸Ca,xn)^286-x112 were measured to be: σ _3n = 2.5_{ - 1.1}^{ + 1.8} pb and σ _4n = 0.6_{ - 0.5}^{ + 1.6} pb ; for the reaction ²⁴²Pu(⁴⁸Ca,xn)^290-x114: σ_2n 0.5 pb, σ _3n = 3.6_{ - 1.7}^{ + 3.4} pb and σ _4n = 4.5_{ - 1.9}^{ + 3.6} pb . In the reaction ²³³U(⁴⁸Ca,2-4n)^277-279112 we measured an upper cross section limit of σ_xn≤0.6 pb. An increase of σ_ER in the reactions of actinide targets with ⁴⁸Ca is consistent with the expected increase of the survivability of the excited compound nucleus upon closer approach to the closed neutron shell N=184. The observed nuclear decay properties of the nuclides with Z=104-118 are compared with theoretical nuclear mass calculations and the systematic trends of α-decay properties. As a whole, they give a consistent pattern of decay of the 18 even-Z neutron-rich nuclides with Z=104-118 and N=163-177.