Formation of superheavy nuclei in cold fusion reactions

Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus, and the de-excitation process are calculated by using an empirical coupled channel model, solving a master equation numerically and applying statistical theory, respectively. Evaporation residue excitation functions in cold fusion reactions are investigated systematically and compared with available experimental data. Maximal production cross sections of superheavy nuclei in cold fusion reactions with stable neutron-rich projectiles are obtained. Isotopic trends in the production of the superheavy elements Z=110, 112, 114, 116, 118, and 120 are analyzed systematically. Optimal combinations and the corresponding excitation energies are proposed.

The role of potential structure in excitation functions of synthesizing superheavy nuclei

The excitation functions of two very similar reaction channels, Fe-58+Pb-208 ->(265)Hs+1n and Fe-58+Bi-209 ->(266)Mt+1n are studied in the framework of the dinuclear system conception. The fusion probabilities are found to be strongly subject to the structure of the driving potential. Usually the fusion probability is hindered by a barrier from the injection channel towards the compound nuclear configuration. The barrier towards the mass symmetrical direction, however, also plays an important role for the fusion probability, because the barrier hinders the quasi-fission, and therefore helps fusion.

Possible way to synthesize superheavy element Z=117

Within the framework of the dinuclear system model, the production of superheavy element Z = 117 in possible projectile-target combinations is analysed systematically. The calculated results show that the production cross sections are strongly dependent on the reaction systems. Optimal combinations, corresponding excitation energies and evaporation channels are proposed, such as the isotopes Bk-248,Bk-249 in Ca-48 induced reactions in 3n evaporation channels and the reactions Sc-45+Cm-246,Cm-248 in 3n and 4n channels, and the system V-51+Pu-244 in 3n channel.

Isotopic dependence of production cross sections of superheavy nuclei in hot fusion reactions

The dinuclear system model has been further developed by introducing the barrier distribution function method in the process of heavy-ion capture and fusion to synthesize superheavy nuclei. The capture of two colliding nuclei, formation and de-excitation process of compound nucleus are decribed by using empirical coupled channel model, solving master equation numerically and statistical evaporation model, respectively. Within the framework of the dinuclear system model, the fusion-evaporation excitation functions of the systems Ca-48(Am-243, 3n-5n) (288-286)115 and Ca-48(Cm-248, 3n-5n)(293-291)116 are calculated, which are used for synthesizing new superheavy nuclei at Dubna in recent years. Isotopic dependence of production cross sections with double magic nucleus Ca-48 bombarding actinide targets U, Np, Pu, Am, Cm to synthesize superheavy nuclei with charged numbers Z=112-116 is analyzed systematically. Based on these analysis, the optimal projectile-target combination and the optimal excitation energy are proposed. It is shown that shell correction energy and neutron separation energy will play an important role on the isotopic dependence of production cross sections of superheavy nuclei.

The influence of nuclear orientation in fusion dynamics

Fusion barriers have been calculated for different orientations of the axial symmetry axis of deformed projectile-and target-nucleus. Using the concept of dinuclear system, considering the strong competition between fusion and quasifission processes, by solving the master equation numerically to calculate the fusion probability of superheavy nuclei, we have estimated the dependence of the fusion probabilities for Ge-76 + Pb-208 and Ca-48 + Pu-244 on the orientation angles of the symmetry axis of projectile-and target-nucleus, which shows that belly-belly is the most favorable orientation for synthesizing superheavy nuclei.

Production of Superheavy Nuclei in Massive fusion reactions

A master equation is constructed to treat the nucleon transfer process in heavy ion fusion reactions to form superheavy nucleus. The relative motion concerning the energy, the angular momentum and the fragment deformation relaxations is explicitly treated to couple with the diffusion process. The nucleon transition probabilities, which are derived microscopically, are thus time dependent. The calculated evaporation residue cross-sections for both cold and hot fusion are in good agreement with the known experimental data.

Production mechanism of superheavy nuclei in massive fusion reactions

Within the concept of the dinuclear system (DNS), a dynamical model is used for describing the formation of superheavy residues in massive fusion reactions, in which the capture of two colliding nuclei, the formation and de-excitation of the compound nucleus are described by using a barrier distribution method, solving master equations numerically and statistical approach, respectively. Using the DNS model, the production cross sections of superheavy nuclei are calculated and compared with the available experimental data. The isotopic dependence of the cross sections to produce the superheavy element Z=116 by the two types of the reactions is discussed and the possible reasons influencing the isotopic trends are analyzed systematically.

Competing fusion and quasifission reaction mechanisms in the production of superheavy nuclei

Within the framework of a dinuclear system model, a new master equation is constructed and solved, which includes the relative distance of nuclei as a new dynamical variable in addition to the mass asymmetry variable so that the nucleon transfer, which leads to fusion and the evolution of the relative distance, which leads to quasifission (QF) are treated simultaneously in a consistent way. The QF mass yields and evaporation residual cross sections to produce superheavy nuclei are systematically investigated under this framework. The results fit the experimental data well. It is shown that the Kramers formula gives results of QF, which agree with those by our diffusion treatment, only if the QF barrier is high enough. Otherwise some large discrepancies occur.

Influence of entrance channels on the formation of superheavy nuclei in massive fusion reactions

Within the framework of the dinuclear system (DNS) model, the production cross sections of superheavy nuclei Hs (Z=108) and Z=112 combined with different reaction systems are analyzed systematically. It is found that the mass asymmetries and the reaction Q values of the projectile target combinations play a very important role on the formation cross sections of the evaporation residues. Both methods to obtain the fusion probability by nucleon transfer by solving a set of microscopically derived master equations along the mass asymmetry degree of freedom (ID) and distinguishing protons and neutrons of fragments (2D) are compared with each other and also with the available experimental data. (C) 2010 Elsevier B.V. All rights reserved.

基于双核模型对合成超重元素反应机制的研究

超重元素的合成是当前原子核物理研究的前沿领域之一。现有的兰州重离子加速器系统为我们提供了在实验上进行超重核研究的可能性。本论文就是为配合在兰州重离子加速器国家实验室开展这方面的物理工作而进行的理论研究。主要内容包括： （1） 我们分别采用数值和解析的办法计算了重离子碰撞过程中核作用势与库仑能，对双核模型中的粒子势能面进行了比较。 （2） 在模型的框架内，考虑了熔合与准裂变的竞争，对描述质量输运过程的主方程进行数值求解。求解是时间相关的，与径向动能、角动量以及形变的弛豫过程相耦合。 （3） 在双核模型基础上引入了Kramers 公式，计算了准裂变碎片的质量分布，得到了与实验符合的结果。提取出了碎片质量分布随时间的演化关系，为理解熔合与准裂变竞争过程提供了非常有用的信息。 （4）用统计模型对带有激发能的复合核的存活概率进行了研究。计算了合成超重元素的蒸发剩余截面，得到与实验符合很好的结果。 （5） 计算了核对称轴不同相对取向时的熔合位垒以及核对称轴不同相对取向对熔合概率的影响。结果表明不同的相对取向对熔合反应的影响较大，并发现弹靶碰撞为腰对腰时，更有利于发生熔合反应

Dinuclear Ru-Cu complexes : electronic characterisation and application to dye-sensitised solar cells

Dye-sensitised solar cells have emerged as an important developing technology for low-cost solar energy conversion and a crucial element of these is the dye, responsible for light harvesting and control of interfacial electron-transfer processes.[1] A number of examples of dye exist in the literature which link a ruthenium polypyridyl complex to another platinum group metal complex such as Ru (II), Os (II), Re (I) or Rh (III) via a bridging ligand.[2-6] These systems are often referred to as heterosupramolecular triads when adsorbed on the surface of TiO2 as the semiconductor becomes an active component in the system. A number of problems can arise with these types of sensitisers, for example if a flexible linker, e.g. bis-pyridylethane, is used to couple the two complexes it can be hard to control the orientation of the whole dye. This may lead to the resultant dye cation hole being closer to the surface than desired, and hence the long-lived charge-separated state is not achieved. In addition the size of these dyes may be much larger than that of a mononuclear complex and can lead to poor pore filling on the TiO2 and lower dye coverage, leading to a lower efficiency cell.[7] Despite these issues, efficient charge-separation has been achieved with polynuclear complexes and a long-lived state on the millisecond timescale has been observed for a trinuclear ruthenium complex.[8]

A Unique Nickel System having Versatile Catalytic Activity of Biological Significance

A new dinuclear nickel(II) complex, [Ni-2(LH2)(H2O)(2)(OH)(NO3)](NO3)(3) (1), of an ``end-off'' compartmental ligand 2,6-bis(N-ethylpiperazine-iminomethyl)-4-methyl-phenolato, has been synthesized and structurally characterized. The X-ray single crystal structure analysis shows that the piperazine moieties assume the expected chair conformation and are protonated. The complex 1 exhibits versatile catalytic activities of biological significance, viz. catecholase, phosphatase, and DNA cleavage activities, etc. The catecholase activity of the complex observed is very dependent on the nature of the solvent. In acetonitrile medium, the complex is inactive to exhibit catecholase activity. On the other hand, in methanol, it catalyzes not only the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very difficult to oxidize, under aerobic conditions. UV vis spectroscopic investigation shows that TCC oxidation proceeds through the formation of an intermediate. The intermediate has been characterized by an electron spray ionizaton-mass spectrometry study, which suggests a bidentate rather than a monodentate mode of TCC coordination in that intermediate, and this proposition have been verified by density functional theory calculation. The complex also exhibits phosphatase (with substrate p-nitrophenylphosphate) and DNA cleavage activities. The DNA cleavage activity exhibited by complex 1 most probably proceeds through a hydroxyl radical pathway. The bioactivity study suggests the possible applications of complex 1 as a site specific recognition of DNA and/or as an anticancer agent.

A Unique Nickel System having Versatile Catalytic Activity of Biological Significance

A new dinuclear nickel(II) complex, [Ni-2(LH2)(H2O)(2)(OH)(NO3)](NO3)(3) (1), of an "end-off" compartmental ligand 2,6-bis(N-ethylpiperazine-iminomethyl)-4-methyl-phenolato, has been synthesized and structurally characterized. The X-ray single crystal structure analysis shows that the piperazine moieties assume the expected chair conformation and are protonated. The complex 1 exhibits versatile catalytic activities of biological significance, viz. catecholase, phosphatase, and DNA cleavage activities, etc. The catecholase activity of the complex observed is very dependent on the nature of the solvent. In acetonitrile medium, the complex is inactive to exhibit catecholase activity. On the other hand, in methanol, it catalyzes not only the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very difficult to oxidize, under aerobic conditions. UV vis spectroscopic investigation shows that TCC oxidation proceeds through the formation of an intermediate. The intermediate has been characterized by an electron spray ionizaton-mass spectrometry study, which suggests a bidentate rather than a monodentate mode of TCC coordination in that intermediate, and this proposition have been verified by density functional theory calculation. The complex also exhibits phosphatase (with substrate p-nitrophenylphosphate) and DNA cleavage activities. The DNA cleavage activity exhibited by complex 1 most probably proceeds through a hydroxyl radical pathway. The bioactivity study suggests the possible applications of complex 1 as a site specific recognition of DNA and/or as an anticancer agent.

Family of Mixed-Valence Oxovanadium(IV/V) Dinuclear Entities Incorporating N4O3-Coordinating Heptadentate Ligands: Synthesis, Structure, and EPR Spectra

Dinuclear ((VVV)-V-IV) oxophenoxovanadates of general formula [V2O3L] have been synthesized in excellent yields by reacting bis(acetylacetonato)oxovanadium(IV) with H3L in a 2:1 ratio in acetone under an N-2 atmosphere. Here L3- is the deprotonated form of 2,6-bis[{{(2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L1), 2,6-bis[{{(5-methyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L2) 2,6-bis[ {{(5-tert-butyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenoI (H3L3), 2,6-bis[{{(5-chloro-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L4) , 2,6-bis[{{(5-bromo-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L5), or 2,6-bis[{{(5-methoxy-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L6). In [V2O3L1], both the metal atoms have distorted octahedral geometry. The relative disposition of two terminal V=O groups in the complex is essentially cis. The O=V...V=O torsion angle is 24.6(2)degrees. The V-O-oxo-V and V-O-phenoxo-V angles are 117.5(4) and 93.4(3)degrees, respectively. The V...V bond distance is 3.173(5) Angstrom. X-ray crystallography, IR, UV-vis, and H-1 and V-51 NMR measurements show that the mixed-valence complexes contain two indistinguishable vanadium atoms (type 111). The thermal ellipsoids of O2, O4, C10, C14, and C15 also suggests a type III complex in the solid state. EPR spectra of solid complexes at 77 K display a single line indicating the localization of the odd electron (3d(xy)(1)). Valence localization at 77 K is also consistent with the V-51 hyperfine structure of the axial EPR spectra (3d(xy)(1) ground state) of the complexes in frozen (77 K) dichloromethane solution: S = 1/2, g(parallel to) similar to 1.94, g(perpendicular to) similar to 1.98, A(parallel to) similar to 166 x 10(-4) cm(-1), and A(perpendicular to) similar to 68 x 10(-4) cm(-1). In contrast isotropic room-temperature solution spectra of the family have 15 hyperfine lines (g(iso) similar to 1.974 and A(iso) similar to 50 x 10(-4) cm(-1)) revealing that the unpaired electron is delocalized between the metal centers. Crystal data for the [V2O3L1].CH2Cl2 complex are as follows: chemical formula, C32H43O6N4C12V2; crystal system, monoclinic; space group, C2/c; a = 18.461(4), b = 17.230(3), c = 13.700(3) Angstrom; beta = 117.88(3)degrees; Z = 8.

Competing magnetic interactions in a dinuclear Ni(II) complex: Antiferromagnetic O-H center dot center dot center dot O moiety and ferromagnetic N-3(-) ligand

Synthesis, structural characteristics, magnetic studies and DFT calculations in Ni(II) dinuclear complexes containing two bridging N-3(-) and an O-(HO)-O-... linkage reveal the existence of ferromagnetic interactions between Ni(II) centers via N-3(-) ligands and antiferromagnetic interactions through the H-bonded moiety. The overall magnetic behavior of the system depends on the delicate balance between these two competing interactions.