Quasifission at extreme sub-barrier energies

With the quantum diffusion approach the behavior of the capture cross-section is investigated in the reactions $^{92,94}$Mo + $^{92,94}$Mo, $^{100}$Ru + $^{100}$Ru, $^{104}$Pd + $^{104}$Pd, and $^{78}$Kr + $^{112}$Sn at deep sub-barrier energies which are lower than the ground state energies of the compound nuclei. Because the capture cross section is the sum of the complete fusion and quasifission cross sections, and the complete fusion cross section is zero at these sub-barrier energies, one can study experimentally the unique quasifission process in these reactions after the capture.Comment: 3 pages, 3 figure

Nuclear structure calculations with a separable approximation for Skyrme interactions

A finite rank separable approximation for the quasiparticle RPA calculations with Skyrme interactions that was proposed in our previous work is extended to take into account the coupling between one- and two-phonon terms in the wave functions of excited states. It is shown that characteristics calculated within the suggested approach are in a good agreement with available experimental data.Comment: 6 pages, proceedings of the International Symposium on Physics of Unstable Nuclei (ISPUN02), Halong Bay, Vietnam, November 20-25, 200

Fusion cross sections for superheavy nuclei in the dinuclear system concept

Using the dinuclear system concept we present calculations of production cross sections for the heaviest nuclei. The obtained results are in a good agreement with the experimental data. The experimentally observed rapid fall-off of the cross sections of the cold fusion with increasing charge number $Z$ of the compound nucleus is explained. Optimal experimental conditions for the synthesis of the superheavy nuclei are suggested.Comment: 16 pages, LaTeX, including 3 postscript figure

Sub-barrier capture with quantum diffusion approach: actinide-based reactions

With the quantum diffusion approach the behavior of capture cross sections and mean-square angular momenta of captured systems are revealed in the reactions with deformed nuclei at subbarrier energies. The calculated results are in a good agreement with existing experimental data. With decreasing bombarding energy under the barrier the external turning point of the nucleusnucleus potential leaves the region of short-range nuclear interaction and action of friction. Because of this change of the regime of interaction, an unexpected enhancement of the capture cross section is expected at bombarding energies far below the Coulomb barrier. This effect is shown its worth in the dependence of mean-square angular momentum of captured system on the bombarding energy. From the comparison of calculated and experimental capture cross sections, the importance of quasifission near the entrance channel is shown for the actinide-based reactions leading to superheavy nuclei.Comment: 11 pages, 16 figures, Regular Articl

Treatment of competition between complete fusion and quasifission in collisions of heavy nuclei

A model of competition between complete fusion and quasifission channels in fusion of two massive nuclei is extended to include the influence of dissipative effects on the dynamics of nuclear fusion. By using the multidimensional Kramers-type stationary solution of the Fokker-Planck equation, the fusion rate through the inner fusion barrier in mass asymmetry is studied. Fusion probabilities in symmetric 90Zr+90Zr, 100Mo+100Mo, 110Pd+110Pd, 136Xe+136Xe, almost symmetric 86Kr+136Xe and 110Pd+136Xe reactions are calculated. An estimation of the fusion probabilities is given for asymmetrical 62Ni+208Pb, 70Zn+208Pb, 82Se+208Pb, and 48Ca+244Pu reactions used for the synthesis of new superheavy elements.Comment: 29 pages, LaTeX, including 7 postscript figures, to appear in Nucl. Phys.

Cluster Interpretation of Properties of Alternating Parity Bands in Heavy Nuclei

The properties of the states of the alternating parity bands in actinides, Ba, Ce and Nd isotopes are analyzed within a cluster model. The model is based on the assumption that cluster type shapes are produced by the collective motion of the nuclear system in the mass asymmetry coordinate. The calculated spin dependences of the parity splitting and of the electric multipole transition moments are in agreement with the experimental data.Comment: 29 pages, 10 figure

Collinear cluster tripartition as sequential binary fission in the 235^{235}U(nth_{\rm th},f) reaction

The mechanism leading to the formation of the observed products of the collinear cluster tripartition is carried out within the framework of the model based on the dinuclear system concept. The yield of fission products is calculated using the statistical model based on the driving potentials for the fissionable system. The minima of potential energy of the decaying system correspond to the charge numbers of the products which are produced with large probabilities in the sequential fission (partial case of the collinear cluster tripartition) of the compound nucleus. The realization of this mechanism supposes the asymmetric fission channel as the first stage of sequential mechanism. It is shown that only the use of the driving potential calculated by the binding energies with the shell correction allows us to explain the yield of the true ternary fission products. The theoretical model is applied to research collinear cluster tripartition in the reaction $^{235}$U(n$_{\rm th}$,f). Calculations showed that in the first stage of this fission reaction, the isotopes $^{82}$Ge and $^{154}$Nd are formed with relatively large probabilities and in the second stage of sequential fission of the isotope Nd mainly Ni and Ge are formed. This is in agreement with the yield of the isotope $^{68}$Ni which is observed as the product of the collinear cluster tripartition in the experiment.Comment: 20 pages, 9 figure