Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactionsU233,238,Pu242, andCm248+Ca48

Abstract

We have studied the dependence of the production cross sections of the isotopes 112282,283 and 114286,287 on the excitation energy of the compound nuclei 112286 and 114290. The maximum cross section values of the xn-evaporation channels for the reaction U238(Ca48,xn)112286−x were measured to be σ3n=2.5−1.1+1.8pb and σ4n=0.6−0.5+1.6pb; for the reaction Pu242(Ca48,xn)114290−x: σ2n∼0.5pb, σ3n=3.6−1.7+3.4pb, and σ4n=4.5−1.9+3.6pb. In the reaction U233(Ca48,2–4n)112277–279 at E*=34.9±2.2MeV we measured an upper cross section limit of σxn⩽0.6pb. 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 Ca48 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 112282, 112283, 114286, 114287, and 114288. In the decay of 114287(α)→112283(α)→110279(SF), in two cases out of 22, we observed decay chains of four and five sequential α transitions that end in spontaneous fission of Sg271(Tα∕SF=2.4−1.0+4.3min) and Rf267(TSF∼2.3h), longer decay chains than reported previously. We observed the new nuclide 116292(Tα=18−6+16ms,Eα=10.66±0.07MeV) in the irradiation of the Cm248 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.Received 9 August 2004Corrected 28 January 2005DOI:https://doi.org/10.1103/PhysRevC.70.064609©2004 American Physical Society