Measurement of the fusion probability, PCN, for hot fusion reactions

Background: The cross section for forming a heavy evaporation residue in fusion reactions depends on the capture cross section, the fusion probability, PCN, i.e., the probability that the projectile-target system will evolve inside the fission saddle point to form a completely fused system rather than reseparating (quasifission), and the survival of the completely fused system against fission. PCN is the least known of these quantities. Purpose: We want to determine PCN for the reactions of 101.2 MeV 18O, 147.3 MeV 26Mg, 170.9 MeV 30Si, and 195.3 MeV 36S with 197Au. Methods: We measured the fission fragment angular distributions for these reactions and used the formalism of Back to deduce the fusion-fission and quasifission cross sections. From these quantities we deduced PCN for each reaction. Results: The values of PCN for the reactions of 101.2 MeV 18O, 147.3 MeV 26Mg, 170.9 MeV 30Si, and 195.3 MeV 36S with 197Au are 0.66, 1.00, 0.06, and 0.13, respectively. Conclusions: The new measured values of PCN agree roughly with the semiempirical systematic dependence of PCN upon fissility for excited nuclei.