Experiments on the synthesis of superheavy elements with Z = 110, 112 via Th-232,U-238+Ca-48 reactions

The investigations of the decay properties and formation cross sections of the heaviest isotopes of the elements 110 ((276-277)110) and 112 ((282-283) 112) were Performed at the Flerov Laboratory of Nuclear Reactions at Dubna with the use of the internal and extracted high intensity Ca-48 beams. Th-2 32 and U-238 targets were used in the experiments. The experiments with int ernal beam probe include the use of fast chemistry for the extraction of th e fraction containing 106 element nuclei from the Th-232 target material an d the off line measurements of the possible correlation chains from the (26 8,269)106 alpha decay acid (264,265)104 spontaneous fission. The Ca-48+U-23 8 reaction was investigated at the VASSILISSA recoil separator. The experim ents were performed at two beam energies leading to excitation energies of 33 and 39 MeV. The collected beam doses were 3.5x10(18) and 2.2x10(18), res pectively. Two spontaneous fission events were observed at the lower beam e nergy, which tentatively were assigned to the new neutron rich isotope (283 )112 produced by the reaction U-238(Ca-48,3n)(283)112. The measured cross-s ection is (5.0(-3.2)(+6.3) ) pb and the half-life is (81(-32)(+147)) s. No event was observed at the higher beam energy resulting in an upper cross-se ction limit of 7.3 pb for the 4n evaporation channel.