Prescission Particle Emission of Heavy Nuclei and the Probe of Postsaddle Friction

The stochastic Langevin model is applied to calculate the evolution of postsaddle emitted neutrons, protons and \alpha particles of heavy ²⁴⁰Am nuclei with the postsaddle friction strength( \beta ). A significantly enhanced sensitivity of these particles to \beta has been observed at a high energy( E^* ) and a large angular momentum( \ell ). Moreover, the postsaddle emission as a function of \beta is compared under two contrasting initial conditions of (high E^* , low \ell ) and (low E^* , high \ell ) for the populated ²⁴⁰Am system. It is shown that for the former type of conditions, the influence of friction on particle evaporation is amplified and the sensitivity of light charged particles to friction is significantly increased. These results suggest that in experiment, to precisely probe the postsaddle friction through the measurement of particle multiplicity, in particular light charged-particle multiplicities, it is best to choose intermediate-energy heavy-ion collisions to produce highly excited heavy fissioning nuclei.