4 research outputs found
Excitation functions for Fr208-211 produced in the O-18+Au-197 fusion reaction
Excitation functions for 208\u2013211Fr isotopes produced in the 18O+197Au fusion-evaporation reaction have been measured at Elab=75\u2013130 MeV via characteristic \u3b1 decays by means of an electrostatic deflector and a semiconductor detector. Data have been compared with calculations giving barrier-passing (capture) cross sections and probabilities of the compound nucleus decay into different channels according to the standard statistical model
Fusion of Ca-48+Sm-154 near the Coulomb barrier: enhancement vs. suppression
Fusion-evaporation and fusion-fission cross sections have been measured in the reaction48Ca+154Sm from well below to well above the Coulomb barrier. The comparison of fusion cross sections for this reaction with previous data corresponding to16O+186W, leading to the same compound nucleus202Pb*, puts in evidence an interesting competition between sub-barrier enhancement, due to the strong couplings related to the154Sm deformation, and above barrier suppression for the48Ca induced reaction. The fusion hindrance mechanism has been attributed to the strong quasi-fission component observed in the mass-energy distributions of fission fragments
The peculiarities of the production and decay of superheavy nuclei
The interest in the study of the fission process of superheavy nuclei mainly deals with the opportunity to obtain information about the crossâsection of the compound nucleus (CN) formation at excitation energies Eââ15â30 MeV. It allows one to estimate the survival probability of the superheavy composite system after evaporation of 1â3 neutrons, i.e. in âcoldâ or âwarmâ fusion reactions. However, in order to solve this problem deeper understanding of the coalescence processes between colliding nuclei, the competition between fusionâfission and quasiâfission processes is needed. The characteristics of both processes, their manifestation in the experimental observables and the relative contribution to the capture crossâsection in dependence on the excitation energies, reaction entrance channel etc were investigated for a wide range of targetâprojectile combinations. Results of the experiments devoted to the study of the fusionâfission and quasiâfission processes in the reactions of the formation of the superheavy nuclei with Z = 102â122 are presented. The heavy ions 26Mg, 48Ca, 50Ti, 58Fe and 64Ni were used as projectiles. The choice of the reactions with 48Ca and actinideâtargets 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 projectileâtarget combinations lead to the synthesis of even heavier elements. The experiments were carried out at the Uâ400 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 timeâofâflight 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 fusionâfission and the competitive process of quasiâfission are discussed. The recent results on synthesis of superheavy nuclei and the perspectives of the âhotâ fusion reaction for the production of superheavy nuclei are considered
Shell effects in fission and quasi-fission of heavy and superheavy nuclei
Results of the experiments aimed at the study of fission and quasi-fission processes in the reactions 12C+204Pb,48Ca+144,154Sm,168Er,208Pb,244Pu,248Cm;58Fe+208Pb,244Pu,248Cm, and64Ni+186W,242Pu are presented in the work. The choice of the above-mentioned reactions was inspired by recent experiments on the production of the isotopes283112,289114 and283116 at Dubna [1],[2] using the same reactions. The58Fe and64Ni 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[3] and the neutron multi-detector DEMON[4],[5]. The role of shell effects and the influence of the entrance channel on the mechanism of the compound nucleus fusion-fission and the competitive process of quasi-fission are discussed