[en] The authors discuss the possibility of the observation of geometric effects at the statical deformation of the colliding nuclei by studying the excitation functions in heavy ion fusion reactions. (HSI)

[en] Fusion excitation functions for the systems ⁴⁰Ar+sup(112,116,122)Sn and ⁴⁰Ar+sup(144,148,154)Sm have been determined, covering cross sections ranging from several hundred mb down to the μb level. The data show a pronounced correlation of the subbarrier behaviour with low-energy collective properties of the nuclei involved and are well reproduced by simplified coupled-channel calculations coupling fusion to inelastic channels. The possibilities of parameterizing the data in terms of a simple dynamic barrier-fluctuation phenomenon are discussed and result in the prediction of remarkably diffuse partial-wave distributions above the barrier. This is shown to be important for the analysis of deexcitation phenomena following fusion reactions. (orig.)

[en] In the last years we have developed a technique, which permits the identification of single nuclei with lifetimes down to 10^-₆ s and production cross sections far below the nanobarn region. At SHIP we investigated the elements Fm, Md, 104, 105, 107, and 109 by fusion of Pb or Bi nuclei with ₄₀Ar, ₅₀Ti, ₅₄Cr, or ₅₈Fe projectiles, respectively. The projectile energies were chosen close to the Coulomb-barrier. With these target-projectile combinations, cold compound systems with excitation energies of 20 MeV and less could be formed. So even for the heaviest and most fragile nuclei a small but reasonable chance exists to survive the strong fission competition in the deexcitation of the compound system. (orig./HSI)

[en] Our recent identification of element 107 by α-decay chains with the velocity filter SHIP at GSI Darmstadt has encouraged us to look for even heavier elements. In an irradiation of ²⁰⁹Bi targets with accelerated ⁵⁸Fe ions we found a decay chain consisting of two consecutive alpha desintegrations followed by fission. This decay chain most probably originates from the isotope ²⁶⁶109. (orig.)

No abstract available

[en] Fusion excitation functions for the systems ⁴⁰Ar+sup(112,116,122)Sn and ⁴⁰Ar+sup(144,148,154)Sm have been determined, covering cross sections ranging from several hundred mb down to the μb level. The data show a pronounced correlation of the subbarrier behaviour with low-energy collective properties of the nuclei involved and are well reproduced by simplified coupled channels calculations coupling fusion to inelastic channels. Possibilities to parameterize the data in terms of a simple dynamic barrier fluctuation phenomenon are discussed and result in the prediction of remarkably diffuse partial wave distributions above the barrier. This is shown to be important for the analysis of deexcitation phenomena following fusion reactions. (orig.)

[en] Evaporation residues from the fusion reactions ⁴⁸Ca+^206,208Pb and ⁵⁰Ti+^207,208Pb, ²⁰⁹Bi were investigated using the velocity filter SHIP. Four new isotopes ^258,257105 and ^254,253Lr were identified and α decay of ²⁵⁵104 and ²⁵⁶104 was observed for the first time. A hindrance to complete fusion by a factor of about 30 at bombarding energies close to the classical barrier was deduced from a measured excitation function for ⁵⁰Ti+²⁰⁸Pb. The mass extents for ²⁵⁶104 and ²⁶⁰106, obtained from their α-decay energies, were used to determine the ground-state shell effects and a semi-empirical description of the half-life T_SF for even-even nuclei. The abrupt decrease in T_SF for elements from nobelium to element 104 was found to be correlated with a decrease in the fission barrier width, which we regard as confirmation of the expected drop in the outer fission barrier to below the ground state. The total kinetic energies released in SF of ²⁵⁶104 and ²⁵⁸104 were measured and found to be 207±13 MeV and 220±15 MeV respectively. These values agree with those predicted from empirical systematics. (orig.)

[en] A search for superheavy elements which are expected to occur around the predicted nuclear shell closures at atomic number 114 and neutron number 184 was made in bombardments of ²⁴⁸Cm with ⁴⁸Ca ions. We have carried out this search at energies close to the Coulomb barrier to keep the excitation energy of the compound nucleus Z=116, A=296 as low as possible. The experiments were performed at the accelerators SUPERHILAC (Lawrence Berkeley Laboratory (LBL)) and UNILAC (GSI) and used a variety of improved physical and chemical techniques for the isolation and detection of superheavy elements to increase the sensitivity relative to earlier experiments. The small-angle separator system (SASSY) at LBL and the separator for heavy-ion reaction products (SHIP) at GSI were used for shortlived nuclides, and several radiochemical techniques were applied for longer half-lives. Although a broad range of half-lives, 10^-6 to 10⁸ s, and excitation energies, 16 to 40 MeV, has been examined, no evidence for the formation of superheavy elements with cross sections greater than 10^-34 to 10^-35 cm² was found. (orig.)