Fission lifetime studies are performed using the “neutron-clock” technique associated with statistical and dynamical model calculations. In this framework we have undertaken, at the Louvain-la-Neuve cyclotron facility, the study of ${}^{20}\mathrm{Ne}{+}^{159}\mathrm{Tb}$ and ${}^{20}\mathrm{Ne}{+}^{169}\mathrm{Tm}$ induced fission reactions between $E/A=8\mathrm{}$ and 16 MeV. In this work we have determined (a) fusion-evaporation and fusion-fission cross sections; (b) the prescission and postscission multiplicities of evaporated light particle (neutron, proton, and alpha) and their energy and angular distributions, and (c) the total energy balance of fission process after taking into account preequilibrium or incomplete-fusion processes. The comparison of the experimental data, multiplicities, and cross sections, with the statistical-model calculations incorporating simple aspects of the dynamics have enabled us to determine the ranges of fission lifetimes and the contribution of fast fission at different compound-nucleus excitation energies.

• Received 21 May 2003

DOI:https://doi.org/10.1103/PhysRevC.68.034613