Role of N/Z in Pre-scission Neutrons as an Observable of Nuclear Friction

A dynamical Langevin model is employed to evaluate the excess of the neutron emission in the fission of heavy nuclei 240Cf, 246Cf, 254Cf, 240U relative to the standard statistical-model prediction at various saddle-to-scission friction strengths. It is shown that when the neutron-to-proton ratio N/Z of the system increases, the sensitivity of the excess to the friction decreases substantially, and it almost disappears for 240 U. We suggest that using those compound systems with low N/Z favors an accurate determination for the saddle-to-scission friction strength based on the measurement of the pre-scission neutron multiplicity. (nuclear physics)