Comparative analysis of the energy dependences of the induced fission times for the Pb-like and U-like nuclei obtained by the crystal blocking technique

Comparative analysis of the experimental data on the induced fission lifetimes for the Pb-like and U-like nuclei produced in the 208Pb + 28Si and 238U + 28Si reactions obtained by the crystal blocking technique was performed, within the dynamical approach based on Langevin equations taking into account light particle emission from the hot fissioning system. A discussion of the energy dependence of the time values for U-like nuclei allows to obtain information on the magnitude of nuclear viscosity

Dynamical analysis of the induced fission time obtained by the crystal blocking technique for the 235U + α reaction

The crystal blocking technique has been used to measure the total time of the induced fission process for the 235U + α reaction in the energy rage of bombarding α-particles from 25.9 to 31.2 MeV. The experimental fission lifetimes observed in this reaction vary from 10-17 to 10-16 s, depending on the projectile energy. The experimental data (along with the corresponding data on the angular anisotropy and fissionability of Pu isotopes produced in the investigated reaction) have been analyzed within the dynamic-statistical approach with allowance for the nuclear dissipation phenomenon and the double-humped fission barrier model. It is demonstrated that the time of induced fission reaction at low excitation energies is sensitive to the nuclear viscosity

Pre-equilibrium effects in the secondary particle spectra in the reactions with heavy ions

Theoretical description of the experimentally obtained spectra for protons and alpha-particles and model calculations for the neutron spectra in the reactions with heavy ions has been presented. The hybrid model of non-equilibrium processes was used. Equilibrium evaporation process was analyzed in the framework of the statistical theory of nuclear reactions with Monte-Carlo simulation including certain dynamical and kinematical characteristics. This approach was included in PACE code, which permits to simulate Monte-Carlo de-excitation nuclear process. The Fermi-gas model and level-density phenomenological model for the variation of the nuclear level density parameters was used. In this approach data on O-16+Sn-116 reaction with E-beam=130, 250 MeV were analyzed. Double-differential light charged particle spectra for this reaction were measured using the GARFIELD apparatus in coincidence with evaporation residues. The experimental data were collected in four angular ranges from 29 to 41, 41 to 53, 53 to 67 and 67 to 82 degrees in the laboratory system. The results of the calculations are shown and discussed for these four angular ranges. The contributions from the evaporative and pre-equilibrium processes were analyzed in connection with different nucleus equilibration mechanisms

Double-differential spectra of the secondary particles in the frame of pre-equilibrium model

An approach was developed to describe the double-differential spectra of secondary particles formed in heavy-ion reactions. Griffin model of nonequilibrium processes was used to account for the nonequilibrium stage of the compound system formation. Simulation of de-excitation of the compound system was carried out using the Monte-Carlo method. Analysis of the probability of neutron, proton, and alpha-particle emission was performed both in equilibrium, and in the pre-equilibrium stages of the process. Fission and gamma-ray emission were also considered after equilibration. The analysis of the experimental data on the double-differential cross sections of p, alpha particles for the O-16 + Sn-116 reaction at the oxygen energy E = 130 and 250 MeV were performed

Pre-equilibrium α-particle emission as a probe to study α-clustering in nuclei

A theoretical approach was developed to describe secondary particle emission in heavy ion collisions, with special regards to pre-equilibrium α-particle production. The probabilities of neutron, proton and α-particle emission have been evaluated for both the equilibrium and pre-equilibrium stages of the process. Effects due the possible cluster structure of the projectile which has been excited during the collisions have been experimentally evidenced studying the double differential cross sections of p and α-particles emitted in the E=250MeV 16O +116Sn reaction. Calculations within the present model with different clusterization probabilities have been compared to the experimental data