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.

Study of the mechanism for synthesizing superheavy nuclei based on dinuclear system

Based on the concept of dinuclear system, considering the strong competition between fusion and quasiffision processes, by solving the master equation numerically to calculate the fusion probability of superheavy nuclei, we have estimated the excitation functions for the reactions Ti-50, Fe-58 + Pb-208, Bi-209, and the experimental data are basically reproduced. For different incident energies and different angular momentum, the effects on fusion and survival probability and the contribution to evaporation residue cross section have been given. These results help to further understand the mechanism for, synthesizing superheavy nuclei.

New development of advanced superconducting electron cyclotron resonance ion source SECRAL (invited)

Superconducting electron cyclotron resonance ion source with advance design in Lanzhou (SECRAL) is an 18-28 GHz fully superconducting electron cyclotron resonance (ECR) ion source dedicated for highly charged heavy ion beam production. SECRAL, with an innovative superconducting magnet structure of solenoid-inside-sextupole and at lower frequency and lower rf power operation, may open a new way for developing compact and reliable high performance superconducting ECR ion source. One of the recent highlights achieved at SECRAL is that some new record beam currents for very high charge states were produced by 18 GHz or 18+14.5 GHz double frequency heating, such as 1 e mu A of Xe-129(43+), 22 e mu A of Bi-209(41+), and 1.5 e mu A of Bi-209(50+). To further enhance the performance of SECRAL, a 24 GHz/7 kW gyrotron microwave generator was installed and SECRAL was tested at 24 GHz. Some promising and exciting results at 24 GHz with new record highly charged ion beam intensities were produced, such as 455 e mu A of Xe-129(27+) and 152 e mu A of Xe-129(30+), although the commissioning time was limited within 3-4 weeks and rf power only 3-4 kW. Bremsstrahlung measurements at 24 GHz show that x-ray is much stronger with higher rf frequency, higher rf power. and higher minimum mirror magnetic field (minimum B). Preliminary emittance measurements indicate that SECRAL emittance at 24 GHz is slightly higher that at 18 GHz. SECRAL has been put into routine operation at 18 GHz for heavy ion research facility in Lanzhou (HIRFL) accelerator complex since May 2007. The total operation beam time from SECRAL for HIRFL accelerator has been more than 2000 h, and Xe-129(27+), Kr-78(19+), Bi-209(31+), and Ni-58(19+) beams were delivered. All of these new developments, the latest results, and long-term operation for the accelerator have again demonstrated that SECRAL is one of the best in the performance of ECR ion source for highly charged heavy ion beam production. Finally the future development of SECRAL will be presented.

~(12)C与~(209)Bi反应中Au同位素的产额与Q_(gg)的关系；Q_(gg)-Yield Dependence of Au Isotopes in Interaction of 47 MeV/u ~(12)C With ~(209)Bi

用47MeV/u12C离子轰击天然铋靶,通过炮弹和靶核之间的核子转移反应产生Au同位素。使用放射化学方法从大量Bi和复杂反应产物中分离、纯化Au,并制备Au的γ射线测量源。使用HPGe探测器测量放射性Au同位素的γ活性。根据照射结束时Au同位素的活度和其他相关数据,确定每个Au同位素的产生截面。分析发现,缺中子Au同位素的产生截面与Qgg值之间不遵从指数依赖关系,这可用重离子碰撞中的次级过程加以解释。

47MeV/u~(12) C轰击~(197)Au和~(209)Bi引起的裂变关联测量

本论文的工作：利用两体裂变角关联技术，辅之以飞行时间测量，测定了47MeV/u的~(12)C轰击~(197)Au和~(209)Bi靶中心碰撞对应的线性动量转移（LMT），得到了关联裂片出射的共面歧离分布，同时还发现了关联角很小且共面歧离很大的裂变事件，并得到了其相对速度分布。从测到的LMT分布中，得到中心碰撞对应的最可几线性动量转移约占入射动量的65％，相应于单核子线性动量转移约为192MeV/c.A，进而还估算出了所形成热核的激发能上限。在对关联裂片出射的共面歧离效应研究中，发现了共面歧离宽度是热核激发能的较好量度之一。并给出了共面歧离宽度跟热核单核子激发能的经验关系；还用简化的裂片级联蒸发模型估算了蒸发中子、质子和α粒子的平均多重性

25MeV/u~(40)Ar~(15+)+~(209)Bi反应的裂变研究

本文首先回顾了重离子物理学的发展简史，并介绍了当前的一些关于重离子反应的理论方法，同时对于现在核物理的研究热点，热核的特性进行了概括性的叙述．由于裂变是作者工作的重点，因此在文章中，对裂变反应的理论也进行了介绍．为了能够清楚全面的说明我们的工作，本文对于实验装置和探测器也给出了详细的描述．最后，文章对25 MeVu Ar+Bi反应中的裂变进行了讨论．在这些讨论中，我们分析了反应中与裂变相关的数据，得到了碎片的质量，动能分布。同时运用与碎片相关联的4He粒子能谱提取了核温度和裂前裂后的4He粒子多重性，并利用这一数据计算了不同初始激发能下的裂点激发能和裂变时标.

Collapsed isoparametric element as a singular element for a crack normal to the bi-material interface

It is shown that the variable power singularity of the strain field at the crack tip can be obtained by the simple technique of collapsing quadrilateral isoparametric elements into triangular elements around the crack tip and adequately shifting the side-nodes adjacent to this crack tip. The collapsed isoparametric elements have the desired singularity at crack tip along any ray. The strain expressions for a single element have been derived and in addition to the desired power singularity, additional singularities are revealed. Numerical examples have shown that triangular elements formed by collapsing one side lead to excellent results.

A delay model for noise-induced bi-directional switching

Many biological systems can switch between two distinct states. Once switched, the system remains stable for a period of time and may switch back to its original state. A gene network with bistability is usually required for the switching and stochastic effect in the gene expression may induce such switching. A typical bistable system allows one-directional switching, in which the switch from the low state to the high state or from the high state to the low state occurs under different conditions. It is usually difficult to enable bi-directional switching such that the two switches can occur under the same condition. Here, we present a model consisting of standard positive feedback loops and an extra negative feedback loop with a time delay to study its capability to produce bi-directional switching induced by noise. We find that the time delay in the negative feedback is critical for robust bi-directional switching and the length of delay affects its switching frequency.

Bi-doped BaF2 crystal for broadband near-infrared light source

Bi-doped BaF2 crystal was grown by the temperature gradient technique and its spectral properties were investigated. The absorption, emission and excitation spectra were measured at room temperature. Two broadband emissions centered at 1070 and 1500 nm were observed in Bi-doped BaF2 crystal. This extraordinary luminescence should be ascribed to Bi-related centers at distinct sites. We suggest Bi2+ or Bi+ centers adjacent to F vacancy defects are the origins of the observed NIR emissions. (C) 2009 Optical Society of America