Experiments on the synthesis of superheavy elements with Z=110,112 VIA ²³²Th, ²³⁸U+⁴⁸Ca 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 ⁴⁸Ca beams. ²³²Th and ²³⁸U targets were used in the experiments. The experiments with internal beam probe include the use of fast chemistry for the extraction of the fraction containing 106 element nuclei from the ²³²Th target material and the off line measurements of the possible correlation chains from the ^268,269106 α decay and ^264-265 104 spontaneous fission. The ⁴⁸Ca+²³⁸U reaction was investigated at the VASSILISSA recoil separator. The experiments were performed at two beam energies leading to excitation energies of 33 and 39 MeV. The collected beam doses were 3.5x 10¹⁸ and 2.2x 10¹⁸, respectively. Two spontaneous fission events were observed at the lower beam energy, which tentatively were assigned to the new neutron rich isotope ²⁸³112 produced by the reaction ²³⁸U(⁴⁸Ca,3n)²⁸³112. The measured cross-section is (5.0 ^+6.3_-3.2) pb and the half-life is (81 ⁺¹⁴⁷_-32) s. No event was observed at the higher beam energy resulting in an upper cross-section limit of 7.3 pb for the 4n evaporation channel.