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We have studied the dependence of the production cross-sections of the isotopes 282, 283112 and 286-288114 on the excitation energy of the compound nuclei 286112 and 290114. The maximum cross-sections of the xn-evaporation channels for the reaction 238 U(48 Ca, xn)286-x112 were measured to be: σ3n = 2.5+1.8-1.1pb and σ4n = 0.6+1.6-0.5pb; for the reaction 242 Pu(48 Ca, xn)290-x114: σ2n ∼ 0.5pb, σ3n = 3.6+3.4-1.7pb and σ4n = 4.5+3.6-1.9pb. In the reaction 233 U(48 Ca, 2-4 n)277-279112 we measured an upper cross-section limit of σxn≤0.6pb. An increase of σER in the reactions of actinide targets with 48Ca can be due to the expected increase of the survivability of the excited compound nucleus upon closer approach to the closed neutron shell N = 184. The observed nuclear decay properties of the nuclides with Z = 104-118 are compared with theoretical nuclear mass calculations and the systematic trends of α-decay 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. [ABSTRACT FROM AUTHOR]

In April-May, 2001, the previously reported experiment to synthesize element 118 using the 208Pb(86Kr,n)293118 reaction was repeated. No events corresponding to the synthesis of element 118 were observed with a total beam dose of 2.6 x 1018 ions. The simple upper-limit cross-sections (1 event) were 0.9 and 0.6 pb for evaporation residue magnetic rigidities of 2.00 Tm and 2.12 Tm, respectively. A more detailed cross-section calculation, accounting for an assumed narrow excitation function, the energy loss of the beam in traversing the target and the uncertainty in the magnetic rigidity of the Z = 118 recoils is also presented. Re-analysis of the primary data files from the 1999 experiment showed the reported element 118 events are not in the original data. The current results put constraints on the production cross-section for synthesis of very heavy nuclei in cold-fusion reactions. [ABSTRACT FROM AUTHOR]

A Monte Carlo random probability analysis developed at LLNL for heavy element research was performed for recent experiments aimed at the synthesis of nuclides with Z≥112 and N≥170, to estimate the probability that observed decay chains were a result of a random event. Low probabilities ( < 10-4% for most decay chains) were found. [ABSTRACT FROM AUTHOR]