Based on a dynamical Langevin equation coupled with a statistical decay model, we calculate the excess of the prescission neutron multiplicity of the heavy nuclei ${}^{240}\mathrm{Cf}$, ${}^{246}\mathrm{Cf}$, ${}^{252}\mathrm{Cf}$, and ${}^{240}\mathrm{U}$ over that predicted by the standard statistical model as a function of the postsaddle dissipation strength. We find that with increasing isospin of the system, the sensitivity of the excess to the dissipation strength decreases substantially. Moreover, for ${}^{240}\mathrm{U}$, this excess is no longer sensitive to the nuclear dissipation. These results suggest that, on the experimental side, to accurately obtain information of the postsaddle dissipation strength by measuring the neutron multiplicity evaporated during the fission process of heavy nuclei, it is best to populate those compound systems with low isospin.

• Received 5 January 2009

DOI:https://doi.org/10.1103/PhysRevC.79.031601