Search of the decay of the heaviest isotopes of element 112

To produce heavy isotopes of element 112 in the reaction 48Ca + 238U two experiments at different beam energies were performed. In the first experiment the beam energy at the middle of the target was 231 MeV which leads to the production of the compound nucleus 286112 with an excitation energy of Ex = 33 MeV. In a 20 - day irradiation of the 238U target with a beam dose of 3.5 x 1018 on the focal plane of the recoil separator VASSILISSA two spontaneous fission events were detected. No α-particle emission preceding spontaneous fission nor α-α correlation in the energy range from 8 to 13 MeV in the time interval of up to 10000 s. have been observed. The most probable explanation of the data obtained in this experiment is that the observed spontaneous fission corresponds to the decay of the even-odd isotope (N = 171) of element 112 produced in the reaction 238U (48Ca, 3n)283112 with a cross section of ∼ 5 pb. The half-life of the new spontaneous fission nuclide is about 100 s. In the second experiment the beam energy was 238 MeV which increases the excitation energy of compound nuclei up to Ex = 39 MeV. The total beam dose in that case was 2.2 x 1018. No events due either to spontaneous fission or sequential α-α decay in an energy range from 8 to 12 MeV and the time interval of 1000 s. were detected. These data give the upper limit of 3 pb for the production cross section of the even-even isotope 282112 in the reaction 238U (48Ca, 4n)282112