超重元素合成反应机制研究

回顾了超重元素研究的现状和超重元素合成反应机制研究的发展,指出目前超重元素合成研究中存在的困难和对超重余核鉴别的一些设想.对近对称反应系统的熔合反应机制进行了较深入的讨论,建议对这类反应生成复合核的截面进行理论和实验上的研究.The status and development of the studies on reaction mechanism for synthesis of superheavy elements has been reviewed. In this paper it is pointed out the difficulties existing in the studies and synthesis of superheavy elements and some conceives for measurement and identification of very heavy residues. The fusion of near symmetric reaction systems is discussed and proposed to do more investigations on the fusion cross sections of these reactions on both theory and experiment.     

冷熔合反应合成超重元素的进展

综述了自提出冷熔合反应作为合成原子序数 Z>1 0 6号超重元素的最主要反应机制以来 ,冷熔合合成超重元素所取得的重大成就及其进展至目前所面临的困惑 .详细介绍了最近国际上围绕 1 1 8号元素合成以及对以冷熔合反应合成 Z>1 1 2号超重元素前景上的争论 .讨论了在我国现有实验条件下 ,基于冷熔合机制开展超重元素合成面临的问题. The great successes of cold fusion reaction which was suggested as the most important production mechanism for superheavy element of Z >106, as the well as the main hot point problems in recent research of superheavy element synthesis are reviewed. Some different opinions around the synthesis of the superheavy element of Z =118 and the further prospect of utilizing cold fusion reactions to the syntheses of superheavy elements of Z >112 are introduced in detail...     

Upgrade of RIBLL

The synthesis of the super-heavy nuclei and the study of their properties attract more and more attentions in recent years. The He-jet MG wheel technique with which ^259Db and ^265Bh were synthesized at IMP has reached its limits due to the short life-time and rare amount of the products. In order to identify the nuclei with higher Z, a device for separating the interested nuclei from the heavy background is definitely needed.     

研究重元素原子谱学性质的可能性

论述了重元素,特别是超重元素原子谱学的重要意义。指出了对这些元素原子谱学进行研究的必要性。探讨了通过核反应产生重元素的几率和产额, 以及可能的收集方法,表明了这可为重元素原子谱学研究提供必要的条件。 同时也简单描述了研究重原子谱学的方法——激光共振电离法。 The importance of the atomic spectroscopy of heavy elements,especially the superheavy elements has been briefly reviewed. It is pointed that studies of the atomic spectroscopy of very heavy elements is necessary from the atomic physics and the identification of new superheavy elements. The production probability and yields of heavy elements in the heavy ion induced reactions were discussed. And the possible collection methods for heavy residue of reactions were also retrospected. Those techniques which have been used in the heavy ion reactions and superheavy element identifications will provide some possible support to the studies of heavy element spectroscopy.     

Entrance Channel Dependence of Production Cross Sections of Superheavy Nuclei in Cold Fusion Reactions

Production cross sections of superheavy nuclei Rf and Hs for asymmetric and nearly symmetric projectile-target combinations are systematically studied within the framework of the dinuclear system model. The calculated results show that the production cross sections are strongly dependent on the symmetry of reaction systems. The obtained results are in good agreement with the available experimental data for asymmetric reaction systems.For nearly symmetric systems, the model gives opposite results with coupled channel model in which surface vibration and nucleon transfer are included.     

Enhanced structural and magnetic properties of microwave sintered Li–Ni–Co ferrites prepared by sol–gel method

The properties of lithium ferrites are very sensitive to chemical composition, synthesis method, and sintering techniques. Li–Ni–Co ferrites with compositional formula Li_(0.45-0.5x)Ni_(0.1)Co_xFe_(2.45-0.5x)O_4, where 0.00 ≤ x ≤ 0.1 in steps of 0.02 were prepared by chemical sol–gel method and sintered by microwave sintering technique. The x-ray diffraction patterns confirmed the formation of single phase with spinel structure in all the samples. The structural parameter viz.lattice constant, crystallite size, and x-ray density for these samples were studied and compared with those measured from samples of similar composition prepared by the sol–gel method and sintered by conventional sintering technique. Enhancement in the magnetic properties like Curie temperature, hysteresis parameters was observed by employing sol–gel synthesis combined with microwave sintering. The results obtained and mechanisms involved are discussed in the paper.     

Calculation of decay half-lives for superheavy elements using the double folding model

α decay half-lives of some new synthesized superheavy elements, possibly synthesized superheavy elements and decay products are calculated theoretically within the WKB approximation by using microscopic m-nucleus interaction potentials. These nuclear potentials between the α particle and daughter nuclei are obtained by using the double folding integral of the matter density distribution of the α particle and daughter nuclei with a density-dependent effective nucleon-nucleon interaction, in which the zero-range exchange term is supplemented. The calculated α decay half-lives are compared with those of the different models and experimental data. It is shown that the present calculation successfully provides the half-lives of the observed αdecays for some new superheavy elements and therefore gives reliable predictions for α decay of possibly synthesized superheavy elements in future experiments.     

Calculation of α decay half-lives for superheavy elements using the double folding model＊

α decay half-lives of some new synthesized superheavy elements, possibly synthesized superheavy elements and decay products are calculated theoretically within the WKB approximation by using microscopic α-nucleus interaction potentials. These nuclear potentials between the α particle and daughter nuclei are obtained by using the double folding integral of the matter density distribution of the α particle and daughter nuclei with a density-dependent effective nucleon-nucleon interaction, in which the zero-range exchange term is supplemented. The calculated α decay half-lives are compared with those of the different models and experimental data. It is shown that the present calculation successfully provides the half-lives of the observed decays for some new superheavy elements and therefore gives reliable predictions for α decay of possibly synthesized superheavy elements in future experiments.     

Synthesis of superheavy nuclei with <Superscript>238</Superscript>U target

The production of superheavy nuclei with Z=108-116 via hot fusion reactions of the neutron-rich projectiles with 238U target is systematically studied.The results show that the production cross sections of superheavy nuclei do not decrease monotonously as the atomic number Z increasing.The cross sections of the superheavy nuclei at Z = 112 and 115 are enhanced as compared with the whole Z-trend in synthesis of the superheavy nuclei,which clearly illustrates that the reactions with large negative Q-value and...     

Spherical and Deformed Shell Closures in Superheavy nuclei

The structure of superheavy nuclei has been studied using the macroscopic-microscopic model. The macroscopic energy was calculated with the continuous medium model in which the energy is expressed as a function of nucleon densities. The deformations and structures of superheavy nuclei were systematically investigated. Calculations reproduce well the available data of experimental α-decay energies and half-lives. The investigation of single-particle levels shows that the shell structure is deformation and isospin dependent. Potential-energy-surface calculations display that superheavy nuclei have in general harder shapes than the nuclei of other mass regions.     

超重元素(新核素)合成研究进展情况分析和展望

本文在介绍和分析国际、国内在超重元素 (新核素 )合成实验研究与理论研究进展情况的基础上对我国今后如何从理论与实验的结合上开展超重元素 (核 )合成研究工作提出一些看法和建议 ,提供讨论     

超重元素(新核素)合成研究进展情况分析和展望

本文在介绍和分析国际、国内在超重元素（新核素）合成实验研究与理论研究进展情况的基础上对我国今后如何从理论与实验的结合上开展超重元素（核）合成研究工作提出一些看法和建议，提供讨论。     

Analysis of fusion-fission process with neutron evaporation in superheavy mass region

The fusion-fission process for the synthesis of superheavy elements is discussed on the basis of the fluctuation-dissipation dynamics. We analyze the experimental data using a three-dimensional Langevin calculation. We take the neutron emission into account in the Langevin calculation and compare the results with experimental data. Also we discuss the evaporation residue cross section for superheavy elements.     

Reactions of synthesis of heavy nuclei: Brief summary and outlook

The possible reactions of synthesis of extremely heavy nuclei with almost closed proton and neutron shells are analyzed on the basis of current experimental and theoretical data on the properties of the isotopes of superheavy elements. It has been shown that advances in obtaining extremely heavy nuclei for which microscopic models predict an increase in stability require further investigations of the mechanism of synthesis reactions. Direct and model experiments aimed at solving this problem are discussed.     

Heavy element research at FLNR (Dubna)

The setting of the experiments is described and the results obtained on the synthesis of the heaviest nuclides in reactions induced by ⁴⁸Ca projectiles are presented. The decay properties of the new nuclei confirm the theoretical predictions about the new nuclear shells and the “islands of stability” of superheavy elements. Briefly, also the results of the first experiments aimed to study the atomic and chemical properties of element 112 are reported.     

Binding energies of even-even superheavy nuclei

The structure of the even-even superheavy nuclei with the proton number Z=98–110 is studied using the self-consistent relativistic mean-field theory. The calculated binding energies are in good agreement with the available experimental ones. An upper limit and a lower limit on the binding energies are set by the calculations. This is useful for future calculations of properties of superheavy nuclei and for the experimental synthesis of superheavy nuclei. The energy surface of some relevant superheavy nuclei is also given and it confirms the correctness of the calculations.     

Analysis of fusion-fission process with neutron evaporation in superheavy mass region

The fusion-fission process for the synthesis of superheavy elements is discussed on the basis of fluctuation-dissipation dynamics. Recently, experiments at Dubna on fission of superheavy nuclei were carried out, and the mass and total kinetic energy distributions of fission fragments were measured. The fusion-fission cross section was derived from the experiments. We analyze the data using a three-dimensional Langevin calculation. We present a clear understanding of the competition between the fusion and the quasifission. We emphasize that a one-or two-dimensional model of Langevin calculation is not sufficient to estimate the fusion cross section in the superheavy mass region. Also, experiments on the emission of neutrons in correlation with fission fragments were conducted. It is useful to investigate the fusion-fission dynamics. We take into account the neutron emission with a Langevin calculation and compare it with experimental data. Finally, we discuss the evaporation residue cross section for superheavy elements.     

Study of heavy nuclei at FLNR (Dubna)

Experiments are described and main results presented on the synthesis and decay properties of superheavy nuclides, produced in fusion reactions induced by a ⁴⁸Ca-beam on heavy actinide targets. In such reactions neutron-rich nuclei are formed. For them, according to theory, an abrupt enhancement of stability due to nuclear shell effects is expected. The decay properties of the new nuclides are compared with calculations of theoretical models, which predict the existence of “islands of stability” in the region of hypothetical superheavy elements.