Production and study of heavy neutron rich nuclei formed in multi-nucleon transfer reactions

A new setup is proposed to produce and investigate heavy neutron-rich nuclei located along the neutron closed shell N = 126. This "blank spot" of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes widely used nowadays for the production of exotic nuclei. The present limits of the upper part of the nuclear map are very close to stability while the unexplored area of heavy neutron-rich nuclides along the neutron closed shell N = 126 is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleosynthesis. A new way was recently proposed for the production of these nuclei via low-energy multi-nucleon transfer reactions. The estimated yields of neutron-rich nuclei are found to be rather high in such reactions and several tens of new nuclides can be produced, for example, in the near-barrier collision of 136Xe with 208Pb. This setup could definitely open a new opportunity in the studies at heavy-ion facilities and will have significant impact on future experiments. © 2013 Springer Science+Business Media Dordrecht.status: publishe

The use of SSNTD for the investigation of cluster radioactivity and spontaneous fission

The results of the investigation of some properties of polyethyleneterephtalate, phosphate glass and mica for the study of cluster decay and spontaneous fission of heavy nuclei are given. The investigation results of U-230 cluster decay and Ra-226 spontaneous fission investigation are presented. The probability of U-230 cluster decay in relation to alpha-decay is less than 7.5.10(14). The partial half-life of Ra-226 spontaneous fission is more than 6.6.10(17) yrs. The fusion-fission cross sections for the (Pb-208 + O-16 --> Th-224) reaction, as the inverse reaction of cluster decay, in the subbarrier region of ion energy was measured. For the energies of 78, 75, 73 and 68 MeV O-16 (lab.system) the cross-sections are 7.8; 3.7.10(-2) 8.5.10(-4) and 6.10(-6) mb, respectively

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

Inadequacy of the statistical model: Some evidence for compound nuclei in the A approximate to 150 and E-x approximate to 100-200 MeV region

Light charged-particle multiplicities in the evaporation residue (ER) and fission (FF) channels from the reaction 200 MeV (32)S + (100)Mo as well as ER and FF channel cross-sections have been measured and compared to the predictions of the statistical model (SM) to estimate the fission time scale. The statistical model fails in reproducing the whole set of data and no convincing estimate is possible. In particular, while pre-scission multiplicities can be reproduced, the model strongly overestimates proton and alpha particle multiplicities in the ER channel, irrespective of the SM input parameters and prescriptions used for the level density and the transmission coefficients. Same calculations performed on data from literature in the A approximate to 150 and excitation energy E(x) approximate to 100-200 MeV region, for the ER channel, provide similar conclusions. These findings repropose the problem of the reliability of the SM in describing the compound-nucleus decay and have a relevant impact on the extraction of the fission delay time through the use of the SM

Studies of neutron-rich nuclei with the CLARA-PRISMA setup and description of the heavy-ion detector DANTE

The Clara--Prisma setup is a powerful tool for spectroscopic studies of neutron-rich nuclei produced in multi-nucleon transfer and deep-inelastic reactions. It combines the large acceptance spectrometer Prisma with the \gamma -ray array Clara. Currently at Lnl is being constructed the heavy-ion detector Dante, based on Micro-Channel Plates, that will be installed at the Clara--Prisma setup. Dante will open the possibility of measuring \gamma --\gamma Doppler-corrected coincidences for the events outside the acceptance of Prisma. In this manuscript some results obtained with the Clara--Prisma setup will be discussed, in addition to the description and performance of the first prototype for the heavy-ion detector Dante

Investigation of the reaction Ni-64+U-238 being an option of synthesizing element 120

This study is concerned with the search for entrance channels suitable to synthesize elements with Z > 118. Mass-energy distributions as well as capture cross-sections of fission-like fragments have been measured for the reactions (64)Ni+ (238)U -> (302)U ->(302)120 and (48)Ca + (238)U -> (286)112 at energies near the Coulomb barrier. Compound nucleus fission cross-sections were estimated from the analysis of mass and total kinetic energy distributions. The cross-section drops three orders of magnitude for the formation of the compound nucleus with Z = 120 obtained in the reaction (64)Ni + (238)U compared to the formation of the compound nucleus with Z = 112 obtained in the reaction (48)Ca + (238)U at an excitation energy of the compound nucleus of about 45 MeV. From our analysis it turns out that the reaction (64)Ni + (238)U is not suitable for the synthesis of element Z = 120

Shell effects in Fusion-Fission of heavy and superheavy nuclei

The process of fusion-fission of heavy and superheavy nuclei (SHE) with Z=82 12122 formed in the reactions with 48Ca and 58Fe ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and at the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multi-detector DEMON. As a result of the experiments, mass and energy distributions (MED) of fission fragments, fission, quasi-fission and evaporation residues cross sections, multiplicities of neutrons and \u3b3 quanta and their dependence on the mechanism of formation and decay of compound systems have been studied

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 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

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