A. S. Zubov

Application of statistical methods for analysis of heavy-ion reactions in the framework of a dinuclear system model

Heavy-ion reactions are investigated by statistical methods in the framework of a dinuclear system model (DNS). Synthesis of superheavy elements in cold and hot fusion reactions on Pb and Bi targets, as well as in incomplete fusion reactions, is considered. We also take a look at production of neutron-deficient isotopes and pre-scission neutron emission in quasifission reactions. The results of calculations are compared with the available experimental data. The sensitivity of these results to the method of calculation of the level density and to various theoretical predictions of nuclear properties is analyzed.

Dinuclear systems in complete fusion reactions

Formation and evolution of dinuclear systems in reactions of complete fusion are considered. Based on the dinuclear system concept, the process of compound nucleus formation is studied. Arguments confirming the validity of this concept are given. The main problems of describing the complete fusion in adiabatic approximation are listed. Calculations of evaporation residue cross sections in complete fusion reactions leading to formation of superheavy nuclei are shown. Isotopic trends of the cross sections of heavy nuclei formation in complete fusion reactions are considered.

Possibilities of production of neutron-deficient isotopes of U, Np, Pu, Am, Cm, and Cf in complete fusion reactions

Within the dinuclear system model we analyze the production of yet unknown neutron-deficient isotopes of U, Np, Pu, Am, Cm, and Cf in various complete fusion reactions. Different deexcitation channels of the excited compound nucleus are treated. The results are obtained without special adjustment to the selected evaporation channel. The fusion probability is an important ingredient of the excitation function. The results are in good agreement with the available experimental data. The alpha decay half-life times in the neutron-deficient actinides are discussed.

Production of exotic nuclei in quasifission-type reactions

The possibilities for producing neutron-rich isotopes 82,84,86Zn and 86,88,90,92Ge are demonstrated in the reactions 48Ca+238U, 244Pu at incident energies near the Coulomb barrier. The production cross sections of new neutron-rich isotopes of nuclei with charge numbers Z=64–80 are estimated as well. The dynamics of the binary reaction is considered as the diffusive multinucleon transfer between the interacting nuclei in the collisions when the excitation energy of the produced exotic isotope is lower than the threshold for the neutron emission. In the quasifission reactions 48Ca+244,246,248Cm at beam energies close to the corresponding Coulomb barriers one can produce new isotopes of superheavies with Z = 103–108, which mainly undergo fission.

Population and properties of superdeformed bands in A ∼ 150 region

The production of superdeformed nuclei, treated as cluster configurations in the A ~ 150 region is described in the framework of statistical approach and the dinuclear system concept. The competition of particle emission from the dinuclear system and quasifission is taken into account. The calculated nuclear characteristics of the superdeformed band in 152Dy are close to the experimental values.

Formation of strongly deformed states in entrance channels

The high-spin hyperdeformed (HD) nuclear states treated as dinuclear or quasi-molecular configurations are suggested to be directly populated in heavy ion-collisions at near Coulomb barrier energies.

Isotopic dependence of the cross section for the induced fission of heavy nuclei

The cross sections for the induced fission of 211−223Ra, 203−211Rn, and 221−231Th nuclei undergoing peripheral collisions with 208Pb nuclei are calculated on the basis of the statistical model. The role of the N = 126 neutron shell is studied. The level density in excited nuclei is determined within the Fermi gas model and a model that takes into account the collective enhancement of the level density. The inclusion of a particle—hole excitation in addition to a collective Coulomb excitation makes it possible to obtain a satisfactory description of experimental cross sections for the fission of radium isotopes. The calculated ratios of the cross sections for the induced fission of 236U (237U) and 238U (239U) nuclei agree with experimental data.

Quantum-mechanical description of the initial stage of fusion reaction

Projectile-nucleus capture by a target nucleus at bombarding energies in the vicinity of the Coulomb barrier is treated on the basis of the reduced-density-matrix formalism. The effect of dissipation and fluctuations on the capture process is taken into account self-consistently within this model. Cross sections for evaporation-residue formation in asymmetric-fusion reactions are found by using the calculated capture probabilities averaged over all orientations of the deformed projectile or target nucleus.

Isotopic dependence of induced fission cross sections for heavy nuclei

Using the statistical model, we calculate the induced fission cross sections for the nuclei 211–223Ra in their peripheral collisions with 208Pb. The role of closed shell N = 126 is studied. Level densities of the Fermi‐gas model and of the model with collective enhancement are used. Taking into account the particle‐hole excitation in addition to the collective Coulomb excitation, we obtain satisfactory agreement with the experimental data.

Dynamics in the production of superheavy elements

The dynamics of fusion is described by the dinuclear system concept which assumes two touching nuclei which carry out motion in the internuclear distance and exchange nucleons by transfer. The corresponding model can be applied to calculate evaporation residue cross sections for complete and incomplete fusion reactions leading to superheavy nuclei.