Nucleus-nucleus proximity potential and superheavy nuclei

Using up-to-date values of nuclear radii and of the nuclear surface tension, the 1977 proximity treatment of nucleus-nucleus interaction is confronted with 113 measured fusion barriers. The approximate to 4% overestimate of theory with respect to experiment, seen in a similiar comparison in 1981, is no longer present. The calculated proximity barriers, when applied to fusion reactions used to produce heavy elements with atomic number Z = 102-118, suggest that the unexpectedly large cross section observed in the reaction Kr-86 + Pb-208 --> (293)118 + In may be due to the sinking of the Coulomb barrier below the level of the bombarding energy. Tests of this hypothesis are suggested. Some consequences of the appearance of such unshielded reactions for very heavy systems are discussed. An Appendix supplies very accurate analytic formulas for the universal nuclear proximity force and potential functions phi and Phi. This does away with the need to consult the tables published in 1977.