PRODUCTION AND DEEXCITATION OF HOT NUCLEI IN COLLISIONS OF 27 MEV/NUCLEON AR-40 WITH U-238

Hot nuclei, produced in the reaction 1080 MeV 40Ar+238U, have been studied by means of the light charged particles emitted in coincidence with fission fragments. A dominant fraction of the light charged particles emitted in the backward hemisphere (60%, 75%, 80% and 85% for 1,2,3H and 4He, respectively) comes from evaporation from a composite nucleus prior to scission. Careful analysis of the cross sections and energy spectra of these evaporated particles yields several properties of the hot nuclear emitters: (i) they are thermalized with an average temperature of 4.0-4.6 MeV, (ii) they are quite deformed (mean axis ratio ≈ 2 1) and are rapidly spinning (Jr.m.s. of 100-140 h {combining short stroke overlay} MeV). Predictions from a dynamical model, based on the Landau-Vlasov equation, are consistent with the experimental results, and give insights into the time evolution of the fused system. © 1990.