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The decay of 176,182,188,196Pt* compound systems formed in 64Ni+112,118,124Sn and 132Sn+64Ni reactions is studied by using the well established dynamical cluster-decay model (DCM), with effects of quadrupole deformations (β2) and “optimum” orientations for hot (compact) configurations included. Our calculations indicate that the mass fragmentation yields change from predominantly symmetric to predominantly asymmetric with the increase in number of neutrons in Pt* nuclei. The comparison between the experiments and DCM calculations are excellent for evaporation residue cross-sections at both the below and above barrier energies, but the fission data show a significant quasi-fission component at the highest one or two energies. [ABSTRACT FROM AUTHOR]

We analyzed experimental data obtained for the mass distribution of fission fragments in the reactions 36S+238U and 30Si+238U at several incident energies, which were performed by the JAEA group. Using the dynamical model with the Langevin equation, we precisely investigate the incident energy dependence of the mass distribution of fission fragments. We also consider the fine structures in the mass distribution of fission fragments caused by the nuclear structure at a low incident energy. It is explained why the mass distribution of fission fragments has different features in the two reactions. The fusion cross sections are also estimated. [ABSTRACT FROM AUTHOR]

Fission fragment mass distribution has been measured from the decay of 246Bk nucleus populating via two entrance channels with slight difference in mass asymmetries but belonging on either side of the Businaro Gallone mass asymmetry parameter. Both the target nuclei were deformed. Near the Coulomb barrier, at similar excitation energies the width of the fission fragment mass distribution was found to be drastically different for the 14N+232Th reaction compared to the 11B+235U reaction. The entrance channel mass asymmetry was found to affect the fusion process sharply. [ABSTRACT FROM AUTHOR]

Recently our FLNR theoretical group completes a calculation model to treat all reaction processes in heavy and superheavy mass region, which is so called “Unified model.” Using a lot of available experimental data, we verify the validity of our model and establish a reliable model to describe the whole reaction process. As examples of the application of our model, we discuss two cases that are quasi-fission process and deep inelastic collision. We show the calculation results of the mass distribution of fission fragments in the reaction 36S+236U. Also, we discuss the possibility for the production of new heavy neutron-rich nuclei in the low-energy multi-neutron transfer process. [ABSTRACT FROM AUTHOR]

Mass-angle distributions carry detailed information on the characteristics of quasi-fission, and thus of the dynamics of heavy element formation reactions. Recent experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

As an alternative to the well known Hauser-Feshbach analysis and statistical fission model, a dynamical collective clusterization model, called the dynamical cluster-decay model (DCM), is developed for the decay of hot and rotating compound nuclei (CN) formed in the low-energy heavy ion reactions. The model is a non-statistical description for the decay of a CN to light particles (LPs), intermediate mass fragments (IMFs), fusion-fission (FF) and quasi-fission (QF) (equivalently, capture) processes. The model considers all decay products as dynamical mass motions of preformed fragments or clusters through the interaction barrier, thereby including structure effects of the CN, and is applicable to CN from different mass regions. [ABSTRACT FROM AUTHOR]

Recent experimental data showing the interplay between fusion hindrance effects and the onset of the quasi-fission mechanism are presented. The aim of such investigations is understanding the role of entrance channel properties on the competing fusion-fission and quasi-fission processes, also in connection with the possible implications for superheavy element production. In this context, the role of mass asymmetry, nuclear deformation and shell effects is discussed. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

A realistic microscopically-based quantum approach to the competition between fusion and quasi-fission in a heavy fusing system is applied to several reactions leading to 256No. Fusion and quasi-fission are described in terms of a diffusion process of nuclear shapes through a dynamical collective potential energy landscape which is initially diabatic and gradually becomes adiabatic. The microscopic ingredients of the theory are obtained with a realistic two-center shell model based on Woods-Saxon potentials. The results indicate that (i) the diabatic effects play a very important role in the onset of fusion hindrance for heavy systems, and (ii) very asymmetric reactions induced by closed shell nuclei seem to be the best suited to synthesize the heaviest compound nuclei. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Available data on evaporation residue (ER) production and fission in a wide region of compound nucleus (CN) masses and entrance-channel mass-asymmetry values have been analyzed in search for the “starting point”, where the fusion suppression due to the quasi-fission (QF) effect starts to show up. Comparing cross sections for the ER production and fission in reactions leading to the same CN, but having different values of entrance-channel mass-asymmetry, one can extract the fusion probability for a more symmetric combination with respect to quite an asymmetric one, where no limitation seems to occur. An attempt to find correlations between the fusion probabilities derived for the considered combinations and some entrance-channel characteristics is undertaken. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The interest in the study of the fission process of superheavy nuclei mainly deals with the opportunity to obtain information about the cross-section of the compound nucleus (CN) formation at excitation energies E*≈15–30 MeV. It allows one to estimate the survival probability of the superheavy composite system after evaporation of 1–3 neutrons, i.e. in “cold” or “warm” fusion reactions. However, in order to solve this problem deeper understanding of the coalescence processes between colliding nuclei, the competition between fusion-fission and quasi-fission processes is needed. The characteristics of both processes, their manifestation in the experimental observables and the relative contribution to the capture cross-section in dependence on the excitation energies, reaction entrance channel etc were investigated for a wide range of target-projectile combinations. Results of the experiments devoted to the study of the fusion-fission and quasi-fission processes in the reactions of the formation of the superheavy nuclei with Z = 102–122 are presented. The heavy ions 26Mg, 48Ca, 50Ti, 58Fe and 64Ni were used as projectiles. The choice of the reactions with 48Ca and actinide-targets was inspired by the experiments on the production of the isotopes 283112, 289114 and 283116 in Dubna using the same reactions. The 50Ti, 58Fe and 64Ni projectiles were chosen since the corresponding projectile-target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia) and the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) using the time-of-flight spectrometer of fission fragments CORSET. The role of the shell effects, the influence of the entrance channel asymmetry and the deformations of colliding nuclei on the mechanism of the fusion-fission and the competitive process of quasi-fission are discussed. The recent results on synthesis of superheavy nuclei and the perspectives of the “hot” fusion reaction for the production of superheavy nuclei are considered. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A new framework for comparing fusion probabilities in reactions forming heavy elements is presented, that eliminates both theoretical and experimental uncertainties, and gives new insights into systematic behavior. This should help in predicting favorable reactions to form new heavy nuclei. The framework is firstly applied to the formation of isotopes of Thorium, where it is found that production yields follow a simple systematic behavior. The data consistently show that fusion is inhibited (presumably by quasi-fission) by about a factor of 10 for projectiles ranging from Ar to Sn, with little dependence on shell structure in the projectile, target or compound nuclei. Application to formation of isotopes of Nobelium shows much more drastic changes in fusion probability as a function of entrance-channel conditions. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

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. A unified driving-potential and a unified set of dynamic Langevin-type 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 or emerging into two final fragments. The calculated mass, charge, energy and angular distributions of the reaction products agree well with the corresponding experimental data for heavy and superheavy nuclear systems. Collisions of very heavy nuclei (such as 238U+248Cm) are investigated as an alternative way for production of superheavy elements. Large charge and mass transfer was found in these reactions due to the inverse (anti-symmetrizing) quasi-fission process leading to formation of surviving superheavy long-lived neutron-rich nuclei. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Results of the experiments aimed at the study of fission and quasi-fission processes in the reactions 12C+204Pb, 48Ca+144,154Sm, 168Er, 208Pb, 238U, 244Pu, 248Cm; 58Fe+208Pb, 244Pu, 248Cm, and 64Ni+186W, 242Pu are presented. The choice of the above-mentioned reactions was inspired by the experiments on the production of the isotopes 283112, 289114 and 283116 at Dubna using the same reactions. The 58Fe and 64Ni projectiles were chosen since the corresponding projectile-target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia), the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) and the Accelerator of the Laboratory of University of Jyvaskyla (JYFL, Finland) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multi-detector DEMON. The role of shell effects and the influence of the entrance channel asymmetry and the deformations of colliding nucleus on the mechanism of the fusion-fission and the competitive process of quasi-fission are discussed. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]