Search for production of superheavy elements via fusion after instantaneous fission in the reaction 238U + 208Pb

Superheavy elements (SHE) might be formed via a reaction mechanism called 'fusion after instantaneous fission', which is supposed to occur during the collision of a deformed very heavy nucleus with a spherical one. We bombarded natural uranium targets with lead ions and searched for alpha-emitting and spontaneously fissioning reaction products. Different techniques were used: a rotating wheel, a gas jet system and a radiochemical procedure. No SHE have been found. The upper cross section limits are between 10-33 cm2 and 10-34 cm2 within the half-life range from 1 ms to 1 year. In addition, the production cross sections of some Cm and Cf isotopes and of Am fission isomers determined. (orig.)