Heavy residue formation in 20 MeV/nucleon197Au−12Cand197Au−27Alcollisions

Abstract

The yields and velocity distributions of heavy residues and fission fragments from the reaction of 20 MeV/nucleon ${}^{197}\mathrm{Au}$ with ${}^{12}\mathrm{C}$ and ${}^{27}\mathrm{Al}$ have been measured using the MSU A1200 fragment separator. The mass and isotopic distributions of the reaction products are generally consistent with previously measured radiochemical data. One observes, especially for the Au+Al reaction, the production of very neutron deficient nuclides, possibly including ``new'' nuclei. The heavy-residue velocity distributions can be resolved into components due to fusionlike collisions (incomplete fusion, ${v}_{\mathrm{res}}{/v}_{\mathrm{cn}}\ensuremath{\simeq}0.8)$ along with components due to more peripheral interactions. Fusionlike events were observed that lead to near- and trans-gold species. The observed mass and charge distributions of the fusionlike products, sorted by velocity, are compared with the results of simulations using PACE2 and GEMINI of the decay of the excited incomplete fusion products. The simulations, while reproducing the general features of the data, predict residue distributions that are too neutron deficient relative to the observed distributions. The observed yields of the trans-gold species are not predicted in the simulations.