A triple axes multiple target holder assembly

A triple axes multiple target holder assembly has been designed and fabricated to accommodate 27 targets to be used inside a high vacuum scattering chamber. This target holder assembly has been used satisfactorily in ion solid collision experiments using heavy ion beams from an accelerator.     

A field theoretic approach to the atomic collision problems

It is an endeavour to make field theoretic approach available to the domain of electronic and atomic collision physics. The capacity of QED is demonstrated in explaining atomic collision phenomena in Coulomb gauge and depending on energy, in relativistic Lorentz gauge. Feynman diagrams are used to calculate bound state collision problems in atomic physics.     

中国散裂中子源快循环同步加速器主剥离膜设计

设计了中国散裂中子源(CSNS)快循环同步加速器(RCS)注入区的主剥离膜装置。为降低研制难度和成本,提高运行可靠性,选择了回转体式的结构。根据在线可调性、高稳定性、高定位精度和超高真空等技术难点,给出了CSNS/RCS主剥离膜的具体结构方案和控制方案。利用ANSYS有限元分析软件和材料力学原理,对设备的核心部件不锈钢同步带进行了模拟计算和理论分析。     

Evaluation of carbon stripper foils produced by a nitrogen ion beam sputtering method

Carbon stripper foils having thicknesses in the range of 5–40 μg/cm² have been prepared by a nitrogen ion beam sputtering method and their lifetimes have been tested in the Van de Graaff accelerator facility with 3.2 MeV, Ne⁺ ions. The foils of 21 μg/cm² thickness had the longest mean lifetime of 1350.0 mC/cm² (irradiation dose of 8.4×10¹⁸ atoms/cm²) which was 50 times longer than that of commercial foils. However, foils with other thicknesses had extremely short lifetimes similar to commercial foils. The nitrogen content of the foils of both long and short lifetimes has been determined using elastic scattering of 3 MeV α-particles.     

欧洲核子研究中心发现新物质形态——夸克胶子等离子体存在的证据

介绍和评述了欧洲核子研究中心（CERN）的相对论重离子碰撞的重要实验结果及其物理解释。碰撞初期形成了高温高密系统。能量密度达到了产生夸克胶子等离子体（QGP）的阈值,低质量双轻子增长、J／ψ反常压低和奇异粒子增长等实验现象可以用形成了QGP来解释。但目前的实验还不足以证明已经产生了QGP。     

Charge transfer in keV proton collision with atomic oxygen: Differential and total cross sections

Classical Trajectory Monte Carlo method (CTMC) with the modal interaction potential [1] has been used to simulate the differential, total and partial capture cross sections in proton-oxygen atom collisions in the energy range of 0.5–200 keV. An interesting feature of the calculated differential cross sections (DCS) curve below the scattering angle 0.1^○ is the presence of oscillations showing asymmetry in angular positions. The oscillations in the partial cross sections are explained in terms of swapping effect. The DCS and total cross sections are found to be in good agreement with the experimental as well as other theoretical results.     

200KV重离子加速器及其应用

本文介绍一台采用双潘宁型多电荷重离子源的200kV重离子加速器,简述它在GaP光探测器的研制、聚合物材料和金属材料的离子注入改性等方面的研究与应用。     

Two-pion interferometry at small relative momentum for pion sources with transverse and longitudinal expansions in relativistic heavy ion collisions

A two-pion correlation function at small relative momentum for pion sources with transverse and longitudinal expansions in relativistic heavy ion collisions is obtained using two-pion interferometry at small relative momentum, and the relations between the real and apparent parameters of the pion source are given. The relations can be used to extract both the temperature and the transverse and longitudinal expansion velocities of pion sources and to verify the correctness of relativistic transformation T′=T\sqrt {1-v^2} of temperature in relativistic statistical mechanics and thermodynamics.     

A new method for determining hydrodynamic effects on the collision of two spheres

A sphere falling in a fluid may collide with another sphere falling more slowly if, when the spheres are far apart vertically, the horizontal distance between their centers is less than or equal to a critical radius. Accurate prediction of aerosol particle coagulation requires a good understanding of this process. Previously reported optical techniques for measuring hydrodynamic effects on this phenomenon have inherent difficulties detecting grazing collisions and hence in determining the critical radius. In this work, a novel detection technique is demonstrated and it is shown that the critical radius may be determined from the sound generated by the collision of two spheres in a viscous liquid. The technique is shown to provide a more precise and decisive indication of when hard spheres collide.     

Effective atomic numbers for CoCuNi alloys using transmission experiments

Effective atomic numbers for CuCoNi alloys against changing Ni contents were measured in the X-ray energy range from 15.746 to 40.930 keV. The gamma rays emitted a ²⁴¹Am point source have been send on absorbers to be used transmission arrangement. The X-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. The compositions of the Ni films were determined to be 0.03, 0.47, 0.62, 1.23, 1.22 and 1.6 by a scanning electron microscopy in CuCoNi alloys prepared against changing Ni contents. CoCuNi alloy films were prepared with an electrodeposition technique. Also, the total effective atomic numbers of each alloy were estimated using mixture rule. The measured values were compared with estimated values for alloys.     

Event-by-event efficiency fluctuations and efficiency correction for cumulants of superposed multiplicity distributions in relativistic heavy-ion collision experiments

We performed systematic studies on the effects of event-by-event efficiency fluctuations on efficiency correction for cumulant analysis in relativistic heavy-ion collision experiments. Experimentally, particle efficiencies of events measured under different experimental conditions should be different. For fluctuation measurements, the final event-by-event multiplicity distributions should be the superposed distributions of various type of events measured under different conditions. We demonstrate efficiency fluctuation effects using numerical simulation, in which we construct an event ensemble consisting of events with two different efficiencies. By using the mean particle efficiencies, we find that the efficiency corrected cumulants show large deviations from the original inputs when the discrepancy between the two efficiencies is large. We further studied the effects of efficiency fluctuations for the cumulants of net-proton distributions by implementing the UrQMD events of Au+Au collisions at sNN~(1/2) = 7.7 GeV in a realistic STAR detector acceptance. We consider the unequal efficiency in two sides of the Time Projection Chamber(TPC), multiplicity dependent efficiency, and the event-by-event variations of the collision vertex position along the longitudinal direction(V_z). When the efficiencies fluctuate dramatically within the studied event sample,the effects of efficiency fluctuations have significant impacts on the efficiency corrections of cumulants with the mean efficiencies. We find that this effect can be effectively suppressed by binning the entire event ensemble into various sub-event samples, in which the efficiency variations are relatively small. The final efficiency corrected cumulants can be calculated from the weighted average of the corrected factorial moments of the sub-event samples with the mean efficiencies.     

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.     

高能重离子碰撞中有QGP形成时的多π关联信号

对高能重离子碰撞中有夸克–胶子等离子体(QGP)形成时的多粒子玻色–爱因斯坦关联进行了分析.通过考查多π关联平均强度随事件π多重数的变化表明,当有QGP产生时,多π关联平均强度在某一高多重数区域会有明显的上升;这种信号能够敏感地检测在高能重离子碰撞中少数有QGP形成的高π多重数事件.     

高能重离子加速器次级中子屏蔽的理论估算

用R.Madey等人提出的由核反应参数计算屏蔽的方法,计算了入射离子单核能为0.6、1.2GeV¹²C束轰击厚Cu靶的次级中子屏蔽.当入射离子束流为1×10¹³ions/s时,其前向和侧向混凝土屏蔽厚度分别为9.8、4.8m(对0.6GeV)和11.5、6.9m(对1.2GeV).     

HIAF-BRing的双向涂抹注入模拟

BRing是HIAF工程的主加速器,其设计流强为每个脉冲内的粒子数1×1011个（238U34+）,为了达到此设计流强,注入增益应达到88倍以上。BRing采用了双向涂抹注入方案,其满足BRing的注入增益要求,同时具有注入时间短和累计束分布较均匀而减小了空间电荷效应的特点。双向涂抹注入方案利用水平和垂直两组凸轨磁铁以及倾斜的静电偏转板,在水平相空间和垂直相空间内同时进行涂抹。为了检验双向涂抹注入方案能否达到BRing的设计要求,利用ORBIT程序对双向涂抹注入过程进行了模拟,模拟结果显示,在单次双向涂抹注入113圈的情况下,注入效率为97.7%,注入增益达到110.3倍,满足了BRing流强要求。累积束的分布相对均匀,空间电荷效应引起的工作点漂移约为-0.02,粒子因共振损失风险很小。针对注入束流偏角、切割板角度、工作点偏差和Bump延时等不同注入参数进行了误差分析,结果显示BRing的双向涂抹注入效率对注入参数偏差的容忍度较高。BRing is the main accelerator of High Intensity heavy Ion Accelerator Facility(HIAF) and its design current is 1×1011 particles per pulse (238U34+). To accumulate beams up to the design current, the injection gain has to reach 88. Two planes painting injection scheme is proposed for BRing. This scheme uses a tilted electrostatic septum and 8 bump magnets to paint beams into horizontal and vertical phase space simultaneously. It can inject enough beams into the ring in a short time and paint beams uniformly. The injection process is simulated using ORBIT code and 113 turns is injected into BRing with an injection efficiency of 97.7% which meets the requirement for beam current of BRing. The accumulated beams are distributed uniformly in transverse and hence have a little tune shift of -0.02 which reduces the risk of beam loss due to the resonance. Errors of injection parameters are analysed and the result shows two planes painting injection scheme has a high tolerance for errors of injection parameters.     

Classical model for diffusion and thermalization of heavy quarks in a hot medium: memory and out-of-equilibrium effects

We consider a simple model for the diffusion of heavy quarks in a hot bath,modeling the latter by an ensemble of oscillators distributed according to either a thermal distribution or to an out-of-equilibrium distribution with a saturation scale.In this model it is easy to introduce memory effects by changing the distribution of oscillators:we model them by introducing a Gaussian distribution,dN/dω.which can be deformed continuously from a δ-function,giving a Markov dissipation, to a broad kernel with memory.Deriving the equation of motion of the heavy quark in the bath,we remark how dissipation comes out naturally as an effect of the back-reaction of the oscillators on the bath.Moreover,the exact solution of this equation allows to define the thermalization time as the time necessary to remove any memory of the initial conditions.We find that the broadening of the dissipative kernel,while keeping the coupling fixed,lowers the thermalization time.We also derive the fluctuation-dissipation theorem for the bath,and use it to estimate the kinematic regime in which momentum diffusion of the heavy quark dominates over drift.We find that diffusion is more important as long as K_0/ε is small,where K_0 and ε denote the initial energy of the heavy quark and the average energy of the bath,respectively.     

Interferometry imaging for the evolving source in heavy ion collisions at HIRFL-CSR energy

Imaging analysis of two-pion interferometry is performed for an evolving particle-emitting source in heavy ion collisions at HIRFL-CSR energy. The source evolution is described by the relativistic hydrodynamics in (2+1) dimensions. The model-independent characteristic quantities of the source are investigated and compared with the interferometry results obtained by the usual Gaussian formula fit. It is found that the first- order source function moments can describe the source sizes. The ratio of the normalized standard deviation σ to the first-order moment R, σ/R, is sensitive to the shape of the source function.     

强流加速器材料研究

加速器技术的快速发展以及科学技术研究和应用的不断需求,使得高流强和高品质成为新一代加速器装置的最重要的指标。目前大型科学实验装置如重离子束驱动的惯性约束聚变装置、对撞机、中微子及介子工厂、散裂中子源等都需要强流加速器。详细介绍了强流加速器中涉及的材料问题以及强流加速器在聚变堆材料研究中的作用和前景。With the increasing development of accelerator technology and the growing requirements from scientific and technical researches as well as applications, high intensity and high performance become the most important characters of the new accelerator facilities. Currently, many large-scale scientific experimental facilities such as the heavy-ion driven inertial confined fusion facility, the collider, the neutrino and muon factories, the spallation neutron source and so on all need the high intensity accelerators. In this paper, the material issues relevant to the high intensity accelerators and the applications of high intensity accelerators are introduced.     

Anisotropic emission of charged mesons and structure characteristic of emission source in heavy ion collisions at 1-2A GeV

Angular distributions of pious and kaons produced in heavy ion collisions at the low-energy end of high energies （1-2 A GeV） have been investigated by using a multisource ideal gas model. The model covers the expansions and movements of the emission sources, and it is related to the collective flows. By using the analytic expression and the Monte Carlo method, the azimuthal and polar angle distributions of mesons are calculated by the model and compared with the experimental data of the KaoS Collaboration.     

A simple technique for laser-induced ablation pressure measurement

A simple method for measuring laser-induced ablation pressure is described. The technique utilizes the well-known double foil concept. In the present experiment the impact times were estimated by monitoring the reflectivity of the impact foil rear. The measurements were performed using a glass laser (1·06 μm wavelength) in the 10¹¹−10¹³ W/cm² irradiance range. Experimental results showed good agreement with those obtained using other techniques as also those with the self-regulating ablation model prediction.