[en] The time scale of the fission process at moderate to high excitation energies is determined by shape-dependent and, most likely, temperature-dependent nuclear dissipation. Most of the present knowledge about the time scale of nuclear fission has been deduced from measurements of multiplicities and the energy spectra of neutrons, light charged particles, and γ-rays evaporated or emitted prior to and after scission. Together with complementary data such as fission probabilities, it is possible to obtain a reasonable description of the time evolution of nuclear fission. The magnitudes of nuclear dissipation, deduced from pre and postscission neutron multiplicities, are compared with the results of recent theoretical dynamical models. The status of the experimental results pointing to a relatively slow fission process and cold scission, as well as the corresponding theoretical interpretation of these findings, are reviewed. 53 refs., 13 figs

[en] Given a picture in which a hot nucleus expands to densities of .2-.4 ρ_o and cools to about T=5 MeV one may investigate the possibility of formation of drops of cold, normal density nuclei. In particular one may apply the nucleation rate formula of Langer and Turski to estimate time scales for such a phenomenon in the context of the nuclear problem

No abstract available

[en] We present a brief review of some static and dynamic properties of metal clusters. We emphasize relations with atomic nuclei and focus on cluster quantities which have counterparts in nuclei. We discuss in particular the case of the optical response which provides a key tool of analysis of the structure and shape of simple metal clusters. We use optical response and corresponding resonant ionization to propose a pump and probe scenario allowing a time resolved analysis of fission in small metal clusters. This gives access to fission time scales in metal clusters in a way similar to measurements of nuclear fission times in hot nuclei. (author)

[en] Nuclear multifragmentation is a new, multibody, decay mode of very hot nuclei. The key properties of this process that were measured are considered, such as the space-time and temperature characteristics. The experimental data for the critical temperature of the nuclear liquid-gas-phase transition are analyzed. Thermal multifragmentation is interpreted as a result of spinodal decomposition, which is actually the specific nuclear liquid-fog-phase transition of the first order.

[en] In [V.E. Viola et al., Phys. Rev. Lett. 93 (2004) 132701, D.S. Bracken et al., Phys. Rev. C 69 (2004) 034612] the observed decrease in spectral peak energies of IMFs emitted from hot nuclei was interpreted in terms of a breakup density that decreased with increasing excitation energy. Subsequently, Raduta et al. [Ad. Raduta et al., Phys. Lett. B 623 (2005) 43] performed MMM simulations that showed decreasing spectral peaks could be obtained at constant density. In this Letter we point out that this apparent inconsistency is due to a selective comparison of theory and data that overlooks the evolution of the fragment multiplicities as a function of excitation energy

[en] The role of dynamics in fission has attracted much interest since the discovery of this process over fifty years ago. However, the study of the dynamical aspects of fission was for many years hampered by the lack of suitable experimental observables against which theoretical calculations could be tested. For example, it was found that the total kinetic energy release in fission can be described equally well by very different dissipation mechanisms, namely the wall formula, that is based on the collisions of the nucleons with the moving wall of the system, as well as a bulk viscosity of the nuclear matter. Although early theoretical work suggested that the fission process may be described as a diffusion process over the fission barrier, this was largely forgotten because of the success of a purely statistical model which instead of enumerating the ultimate final states of the process argues that the fission rate is determined at the open-quote transition state close-quote as the system traverses the fission saddle point. It was therefore significant when Gavron showed that the transition state model was unable to describe the number of neutrons emitted prior to scission at high excitation energy in reactions of ¹⁶O+¹⁴²Nd. Subsequent experimental work using different methods to measure the fission dissipation/viscosity has confirmed these initial observations. It was therefore very surprising when Moretto in recent publications concluded that their analysis of fission excitation functions obtained with a and α and ³He induced projectiles was perfectly in accord with the transition state model and left no room for fission viscosity. In this paper we'll show that Moretto's analysis is flawed by assuming first chance fission only (in direct contradiction to the experimental observation of pre-scission neutron emission in heavy-ion induced fission), and reveal why the systematics presented by Moretto looked so convincing despite these flaws

[en] This review article takes stock of the progress made in understanding the phase transition in hot nuclei and highlights the coherence of observed signatures. (authors)

[en] The isospin effect on particle emission for fissioning isobaric sources of ¹¹0^Tc, ¹¹⁰Pd, ¹¹⁰In and for isotopic sources of ^110,117,124In is explored in the framework of the Smoluchowski equation. A statistical model including dissipation is employed to study particle emission in asymmetric and symmetric fission of the In nucleus with different isospins. Calculations show that for a fissioning nucleus which has a larger isospin, charged particle multiplicities are no longer sensitive to dissipation strength or the fission time scale. Hence, for those systems with very high isospins, protons and α particles cannot be used as probes of the dissipation in the fission of hot nuclei. This conclusion does not depend on the mass asymmetry of the fission process. (author)

[en] The role played by the heaviest fragment in partitions of multifragmenting hot nuclei is emphasized. Its size/charge distribution (mean value, fluctuations and shape) gives information on properties of fragmenting nuclei and on the associated phase transition. (author)