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The focal-plane position spectra and collection efficiencies of the Dubna gas-filled recoil separator at the U400 cyclotron used to separate evaporation residues of complete fusion reaction products are described. The separator consists of a 23°-dipole magnet and a quadrupole doublet and is filled with hydrogen at a pressure of about 1 Torr. After passing through the time-of-flight system, the separated evaporation residues are collected in a 120 mm×40 mm position-sensitive semiconductor detector at the focal plane. Depending on the asymmetry of the projectile, target combinations, the measured collection efficiencies were 3–45%, with suppression factors exceeding 1015 and 104 for beam and target-like particles, respectively. The ANAMARI code that is used to determine the separator settings is described and its predictions for the evaporation residue position spectra and collection efficiencies are compared with experimental data.

The heavy-element research program of the Dubna gas-filled recoil separator requires the use of rather exotic, strongly radioactive targets which can withstand long-term, high-intensity heavy-ion bombardments. A number of targets with thicknesses of 0.1–0.8 mg/cm2 deposited on various backings by different techniques such as electrospraying, mechanical painting with organic solutions, as well as molecular plating or electrodeposition from organic solutions were tested. The best results were obtained for electroplated targets deposited on 1.5 μm Ti backings. Isotopically enriched targets of 235,236,238U, 242,244Pu, and 248Cm mounted on rotating disks were irradiated by ions ranging from neon to argon with intensities up to 2 × 1013pps delivered by the U400 cyclotron. During two months of irradiation the total beam dose of the 34S ions applied to the target of 244Pu reached 2.5 × 1019. Collaborative Dubna-Livermore experiments were performed in 1993–1995 by employing the Dubna gas-filled recoil separator and resulted in the discovery of the new nuclides 262104, 265106, 266106, 267108, and 273110. The experiments aimed at the synthesis of element 114 are under preparation. Target fabrication methods and experimental results for nuclear physics studies at Coulomb energies are described.

In bombardments of 248Cm with 22Ne we discovered two new isotopes, 265106 and 266106, by establishing genetic links between α decays of the 106 nuclides and spontaneous fission (SF) or α decays of the daughter (or granddaughter) nuclides. For 266106 we measured Eα = 8.63 ± 0.05 MeV followed by the SF decay of 262104 for which we measured a half-life value of 1.2+1.00.5 s. For 265106 we measured Eα = 8.71–8.91 MeV. We estimated α half-lives of 10–30 s for 266106 and 2–30 s for 265106 with SF branches of approximately 50% or less. The decay properties of 266106 indicate a large enhancement in the SF stability of this N = 160 nuclide and confirm the existence of the predicted deformed shells N = 162 and Z = 108.

We describe an on-line gas jet system in which the reaction products are transported during 1 s via a thin 6 m tube to a chamber where they are deposited on a jet filter. The fission fragments escaping the filter are registered by ionization chambers that determine their energy and the emission angle. By introducing a correction for energy losses in passive absorbers it is possible to measure the total kinetic energy of fission fragments with an accuracy of 1% for a geometric efficiency of 50%. The prompt neutron multiplicity is measured simultaneously with fission fragment detection.