Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactions233,238U, 242Pu, and248Cm+48Ca

Abstract

We have studied the dependence of the production cross sections of the isotopes 282,283112 and 286,287114 on the excitation energy of the compound nuclei 286112 and 290114. The maximum cross section values of the xn-evaporation channels for the reaction 238U(48Ca, xn)286-x112 were measured to be σ3n = 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: σ2n ∼ 0.5 pb, σ3n = 3.6-1.7+3.4 pb, and σ4n = 4.5-1.9+3.6 pb. In the reaction 233U(48Ca, 2-4n)277-279112 at E* = 34.9=2.2 MeV we measured an upper cross section limit of σxn ≤ 0.6 pb. The observed shift of the excitation energy associated with the maximum sum evaporation residue cross section σER (E*) to values significantly higher than that associated with the calculated Coulomb barrier can be caused by the orientation of the deformed target nucleus in the entrance channel of the reaction. An increase of σER 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. In the present work we detected 33 decay chains arising in the decay of the known nuclei 282112, 283112, 286114, 287114, and 288114. In the decay of 287114(α) → 283112(α) → 279110(SF), in two cases out of 22, we observed decay chains of four and five sequential α transitions that end in spontaneous fission of 271Sg (Tα/SF = 2.4-1.0+4.3 min) and 267Rf (TSF ∼ 2.3h), longer decay chains than reported Sreviously. We observed the new nuclide 292116 (Tα = 18-6+16 ms, Eα = 10.66±0.07 MeV) in the irradiation of the 248Cm target at a higher energy than in previous experiments. The observed nuclear decay properties of the nuclides with Z = 104-118 are compared with theoretical nuclear mass calculations and the systematic trends of spontaneous fission 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. The experiments were performed with the heavy-ion beam delivered by the U400 cyclotron of the FLNR (JINR, Dubna) employing the Dubna gas-filled recoil separator.