Heavy actinide production in the reactions of /sup 238/U+/sup 238/U and /sup 238/U+/sup 248/Cm

Experiments on the production of heavy actinides up to mendelevium from the reactions between /sup 238/U on /sup 238/U and /sup 238/U on /sup 248/Cm are summarized. The authors find that independent of the system and the bombarding energy an average of about 4 neutrons is emitted from the primary fragments implying average excitation energies of 30 to 40 MeV in the heavy fragments. An intercomparison of their data with results obtained with lighter particles like /sup 48 /Ca, /sup 84/Kr and /sup 136/Xe on /sup 238/U and /sup 248/Cm targets, respectively, shows increased formation cross sections for heavy actinides with /sup 238/U as projectile. In addition, for the /sup 238 /U+/sup 238/U reaction cross sections for americium shape isomers are determined. Deduced isomer-to-ground-state ratios are found to be lower as compared to light particle induced reactions. With a simple model estimates of production rates for very heavy elements up to z =104 have been performed for the reactions of /sup 238/U on /sup 248 /Cm, /sup 249/Cf and /sup 254/Es targets. (20 refs).