Cross sections for the production of heavy actinides in damped collisions of 238 U ions with 248 Cm targets are reported and compared with similar data for other projectiles. The relatively small differences in the formation rates of a given isotope made by different projectiles indicate a balance between increased mass transfer probability with increasing projectile mass and a concurrent decrease in survivability because of an increase in excitation energy.

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Nuclear charges and kinetic energies were measured for fragments resulting from reactions of 58 Ni+ 58 Ni and 58 Ni + 197 Au at 15.3-MeV/u incident energy. These data suggest a nonequilibrium division of the available excitation energy between target and projectile for a large range of energy losses. This interpretation is supported by a consistent analysis of more complete data available for the 56 Fe + 165 Ho reaction at 8.5-MeV/u incident energy.PACS numbers: 25.70.Lm, 24.60.-k One of the primary goals in the investigation of inelastic reactions between heavy ions is to understand the mechanism of energy dissipation and nucleon exchange. At incident energies just above the interaction barrier there is evidence 1 ' 2 that the neutron-excess degree of freedom is equilibrated quickly as the charge and neutron number of the primary reaction products move in the direction of the gradient of the two-dimensional dinuclear potential-energy surface. 3 However, recent results for asymmetric systems at energies well above the interaction barrier are not satisfactorily explained in terms of potential-energy-surface considerations alone. 4 " 6 At these energies particle evaporation may dominate the observed distributions which makes it essential to evaluate such effects carefully.We have studied the 58 Ni + 197 Au reaction at 889-MeV incident energy and observe that the charge distributions of the projectilelike fragments are inconsistent with potential-energy-surface expectations unless the available excitation energy is shared equally between the target and projectile, rather than in proportion to their masses, as would have been expected if thermal equilibrium had been attained. Although this is in apparent contradiction to previous conclusions based on comparisons 7 " 10 of neutron emission from the projectilelike fragment (PLF) and targetlike fragment (TLF), it is shown that a careful analysis of such data supports the interpretation of a nonequilibrium energy division for reactions involving incomplete energy damping. These results constitute the first evidence that thermal equilibrium is not immediately attained in damped collisions between heavy ions.The experiment was performed with use of an 889-MeV beam of 58 Ni produced by coupled operation of the tandem electrostatic and cyclotron accelerators of the Holifield Heavy Ion Research Facility in Oak Ridge. Projectilelike fragments resulting from interactions with targets of 58 Ni (1.9 mg/cm 2 ) and of 197 Au (1.2 mg/cm 2 ) were identified by their nuclear charge with a largearea, position-sensitive, gas ionization chamber located 1 m from the target. The ionization chamber was operated with CF 4 gas at a pressure of 500 Torr and subtended 21° in polar angle with a solid angle of 50 msr. It provided AE-AE-E measurement with a total energy resolution of better than 1% for the elastically scattered 58 Ni. The observed fragment energies have been corrected for energy losses in the detector entrance window and in half of the target thickness. Center-of-mass energies wer...

Counter telescope measurements of reactions of 4 Ar+ Ag have been made at laboratory energies between 169 and 337 MeV, Ar+ 2 Sb at 282 and 340 MeV, and Kr+ Cu at 494 and 604 MeV. Measurements and results include elastic scattering, evaporation residue angular distributions and cross sections, fission plus quasifission angular distributions, kinetic energy distributions, and yields versus atomic number. Evaporation residue yields

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