Attempts to produce superheavy elements by fusion of ⁴⁸Ca with ²⁴⁸Cm in the bombarding energy range of 4.5-5.2 MeV/u

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.