Charged particle multiplicities in heavy-ion induced fission

Pre-scission and post-scission multiplicities of protons and α particles are measured in the 16O + 197Au, 19F + 159Tb, 181Ta, 197Au, and 208Pb, and 28Si + 197Au and 208Pb reactions. The observed pre-scission multiplicities are compared to statistical-model predictions. Pre-saddle delay time of 0.5 ∼ 1.5 * 10-20 sec is needed to reproduce both pre-scission proton and α particles. This value is too small to account for the pre-scission neutron data measured by Hinde et al., suggesting a long saddle-to-scission time. The measured post-scission multiplicities of protons and α particles indicate that fission fragments are rather colder than the statistical model prediction, and consistent with the reported post-scission neutron data. The present charged particle data suggest that, as indicated by the reported neutron data, fission is a slow process and a time more than a half of the total fission time scale is spent in the saddle-to-scission region. (authors). 22 refs., 8 figs., 1 tab