Heavy residues and intermediate - mass fragment production in dissipative 197 Au ¿ 86 Kr collisions at E Õ A Ä 35 MeV

Neutrons and charged light and intermediate-mass products from the Au1 Kr reaction at Elab /A 535 MeV were measured with 4p angular coverage, in coincidence with projectilelike ~PLFs! and targetlike fragments ~TLFs!. The characteristics of PLF and TLF yields and their correlation with neutron, light-charged particles, and intermediate-mass fragments ~IMFs! are consistent with a scenario where essentially all collisions proceed through a dissipative stage. It is found that the damping of the available kinetic energy into thermal excitation is essentially incomplete, with no positive evidence for complete damping. Slow, massive reaction products are observed with significant yields. These products, termed also heavy residues, are identified as TLF evaporation residues and as TLF fission fragments. The TLF fission mode is seen to fade away in favor of TLF evaporation residue production for excitation energies above 3–4 MeV/nucleon. The suppression of the TLF fission can be traced to the dynamical IMF production process which reduces considerably the sizes of the primary reaction fragments and, hence, their fissility.