No abstract

From the analysis of appropriate experimental data within a simple theoretical model, it is shown that the intermediate neutron transfer channels with positive Q values really enhance the fusion cross section at sub-barrier energies. The effect is found to be very large, especially for fusion of weakly bound nuclei. New experiments are proposed, which may shed additional light on the effect of neutron transfer in fusion processes.

A new approach is proposed for a unified description of strongly coupled deep inelastic (DI) scattering, fusion, fission and quasi-fission (QF) processes of heavy-ion collisions. The standard (most important) degrees of freedom of the nuclear system, unified driving potential, and a unified set of dynamic equations of motion are used in this approach. This makes it possible to perform a full (continuous) time analysis of the evolution of heavy nuclear systems, starting from the approaching stage, moving up to the formation of the compound nucleus and eventually emerging into two final fission fragments. The calculated mass, charge, energy and angular distributions of the reaction products agree well with the corresponding experimental data. It gives us hope to obtain rather accurate predictions for the probabilities of superheavy element formation in near-barrier fusion reactions.

It is shown that the multinucleon transfer reactions in low-energy collisions of heavy ions may be used for production of new neutron-rich nuclei at the "northeast" part of the nuclear map along the neutron closed shell N=126 which plays an important role in the r process of nucleosynthesis. More than 50 unknown nuclei might be produced in such reactions (in particular, in collision of 136Xe with 208Pb) with cross sections of not less than 1 microb.

The decay properties of 290

A consistent systematic analysis of the synthesis of very heavy nuclei is performed within a ''standard'' theoretical approach without any adjustable parameters and additional simplification. Good agreement with experimental data was obtained in all the cases up to synthesis of the 102 element. It was confirmed that a process of the compound nucleus formation, starting from the instant when two heavy nuclei touch and proceeding in strong competition with the fission and quasifission processes, plays an important role in the asymmetric synthesis of superheavy elements with Z CN у104 as well as in the symmetric fusion at Z CN у90. A new mechanism of the fusion-fission process for a heavy nuclear system is proposed, which takes place in the (A 1 , A 2) space, where A 1 and A 2 are two nuclei, surrounded by a certain number of common nucleons ⌬A. These nuclei gradually lose ͑or acquire͒ their individualities with increasing ͑or decreasing͒ the number of collectivized nucleons ⌬A. The driving potential in the (A 1 , A 2) space is derived, which allows the calculation of both the probability of the compound nucleus formation and the mass distribution of fission fragments in heavy ion fusion reactions.

The dynamics of heavy-ion low-energy damped collisions is studied within the model based on the Langevin-type equations. Shell effects on the multidimensional potential energy surface play an important role in these reactions. An enhanced yield of nuclides far from the projectile and target masses was found in multi-nucleon transfer reactions due to the shell effects. Our theoretical predictions need experimental confirmation.

A thorough analysis of all stages of heavy ion fusion reaction leading to the formation of a heavy evaporation residue has been performed. The main goal of the analysis was to gain better understanding of the whole process and to find out what factors and quantities, in particular, bring major uncertainty into the calculated cross sections, how reliable the calculation of the cross sections of superheavy element formation may be and what additional theoretical and experimental studies should be made in this field.