Studies of heavy-ion reactions and transuranic nuclei

Abstract

The development of the cold-fusion'' episode is reviewed. Ongoing studies of compound-nucleus formation and decay via the neutron multiplicity distribution confirm the validity of conventional statistical theory. The excitation energy partition in near-barrier damped {sup 58}Ni + {sup 208}Pb collisions is found to be largely independent of the direction of net mass transfer, supporting a diffusion-like nucleon-exchange mechanism. Exclusive experiments on the heavy reaction systems {sup 197}Au + {sup 208}Pb and {sup 209}Bi + {sup 136}Xe in the Fermi-energy domain have revealed important new insights into the reaction mechanism, which is found to be dominated by damped, binary processes. The effectiveness of the neutron multiplicity as an impact-parameter filter is demonstrated. It is shown that very-heavy-ion reactions lead to transient nuclear systems with temperatures in excess of {tau} = 6 MeV and transfer of large, aligned spins to reaction fragments. The first measurements of neutrons in coincidence with kinematically identified reaction fragments provide evidence for the binary, sequential character of dissipative collisions in the Fermi-energy domain. Also for the first time, a full event characterization was achieved for nuclear reactions in terms of neutrons and charged particles. Technical information on this experiment is provided. First results yield strong evidence for more » dominantly binary primary reaction dynamics of even highly dissipative {sup 209}Bi + (28MeV/u) {sup 136}Xe collisions, associated with several intermediate-mass fragments. « less