Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactions 233,238U, 242Pu, and 248Cm+48Ca -: art. no. 064609

We have studied the dependence of the production cross sections of the isotopes (282,283)112 and (286,287)114 on the excitation energy of the compound nuclei (286)112 and (290)114. The maximum cross section values of the xn-evaporation channels for the reaction U-238(Ca-48,xn)(286-x)112 were measured to be sigma(3n)=2.5(-1.1)(+1.8) pb and sigma(4n)=0.6(-0.5)(+1.6) pb; for the reaction Pu-242(Ca-48,xn)(290-x)114: sigma(2n)similar to0.5 pb, sigma(3n)=3.6(-1.7)(+3.4) pb, and sigma(4n)=4.5(-1.9)(+3.6) pb. In the reaction U-233(Ca-48,2-4n)(277-279)112 at E*=34.9=2.2 MeV we measured an upper cross section limit of sigma(xn)less than or equal to0.6 pb. The observed shift of the excitation energy associated with the maximum sum evaporation residue cross section sigma(ER)(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 sigma(ER) in the reactions of actinide targets with Ca-48 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 (282)112, (283)112, (286)114, (287)114, and (288)114. In the decay of (287)114(alpha)-->(283)112(alpha)-->(279)110(SF), in two cases out of 22, we observed decay chains of four and five sequential alpha transitions that end in spontaneous fission of (271)Sg (T-alpha/SF=2.4(-1.0)(+4.3) min) and (267)Rf (T(SF)similar to2.3 h), longer decay chains than reported previously. We observed the new nuclide (292)116 (T-alpha=18(-6)(+16) ms,E-alpha=10.66+/-0.07 MeV) in the irradiation of the Cm-248 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.