Narrow Results

In this paper, we applied the Langevin dynamical model to investigate the different aspects of the ${}^{16}$O+${}^{194}$Pt reaction. Elongation and orientation degree of freedom ($K$ coordinate) which are the first and second dimensions of dynamical calculations, are presented here. Fission time, fission cross-section, pre-scission neutron multiplicity, and fission probability were calculated using one- and two-dimensional Langevin equations. Also, anisotropy of fission-fragments angular distribution has been investigated based on the transition state model, one- and two-dimensional Langevin dynamical models. It was found that by adding the orientation degree of freedom to calculations, the fission time and pre-scission neutrons multiplicity increases whereas fission cross-section, and fission probability decreases. The two-dimensional dynamical calculations are a better match to the experimental data than the one-dimensional dynamical calculations, when using nominal values for the reduced dissipation coefficient and shape-dependent level density parameter. However, if model parameters are adjusted to reproduce the fission cross-section data, then both the one- and two-dimensional models give a satisfactory match to the fission fragment anisotropy data. Nonequilibrium $K$ distributions in the dynamical model can better explain the experimental anisotropy of the angular distribution of fission-fragments with respect to the equilibrium $K$ distribution in saddle and scission point transition state models.

The properties of the mass and energy distributions of fissionlike fragments formed in the reactions ³⁶S, ⁴⁸Ca, ⁴⁸Ti, ⁶⁴Ni + ²³⁸U at energies around the Coulomb barrier have been analyzed to define the systematic trend of compound nucleus fission and quasifission in hot fusion reactions with actinide targets. The measurements have been carried out at the U400 cyclotron of the FLNR, JINR using the double-arm time-of-flight spectrometer CORSET. The most probable fragment masses as well as total kinetic energies and their dispersions in dependence on the interaction energies have been investigated for asymmetric and symmetric fragments for the studied reactions. The fusion probabilities have been deduced from the analysis of mass and energy distributions. It was found that for the studied reactions fusion probability depends exponentially on mean fissility parameter of the system. For the reactions with actinide nuclei leading to the formation of superheavy elements the fusion probabilities are of several orders of magnitude higher than in the case of cold fusion reactions.

The properties of the mass and energy distributions of fissionlike fragments formed in the reactions ⁴⁸Ca,⁵⁸Fe + ²⁰⁸Pb, ³⁶S,⁴⁸Ca,⁴⁸Ti,⁶⁴Ni + ²³⁸U, ⁴⁸Ca + ²³²Th,²⁴⁴Pu,²⁴⁸Cm at energies around the Coulomb barrier have been analyzed to define the systematic trend of compound nucleus fission and quasifission in cold and hot fusion reactions. The measurements have been carried out at the U400 cyclotron of the FLNR, JINR using the double-arm time-of-flight spectrometer CORSET. The fusion probabilities have been deduced from the analysis of mass and energy distributions. It was found that for the studied reactions fusion probability depends exponentially on mean fissility parameter of the system. For the reactions with actinide nuclei leading to the formation of superheavy elements the fusion probabilities are of several orders of magnitude higher than in the case of cold fusion reactions.

The main aim of the present study is to evaluate the fusion probabilities and investigate competing quasifission process in the reactions with heavy ions leading to the formation of superheavy composite systems. The mass-energy distributions, as well as capture cross-sections of fission-like fragments for the reactions of ²²Ne, ²⁶Mg, ³⁶S, ⁴⁸Ca, ⁵⁸Fe and ⁶⁴Ni ions with actinides leading to the formation of superheavy compound systems with Z=102-120 at energies near the Coulomb barrier have been measured. The relative contribution of quasifission to the capture cross section becomes dominant for superheavy composite systems. Fusion-fission cross sections were estimated from the analysis of mass and total kinetic energy distributions.