Simulation of Ion Paths in the Target Material for the Injection Complex of the BELA Facility

To realize the simulation experiments with the use of two ion beams at the injection complex of the BELA accelerator (Based on ECR ion source Linear Accelerator), it is necessary to determine the energy and irradiation angle of the beam of light ions which will be implanted into the region of radiation damage induced by heavy-ion beam. The depth of light-ion implantation is determined by the energy and kind of particles initiating the damage, as well as by their incidence angle. It is supposed that the incidence direction of heavy ions will coincide with the normal to the specimen surface. In our work, the necessary implantation zone for the iron ion beam with an energy of 3.2 MeV is located at depths of 300–800 nm. The simulation of the hydrogen and helium ion paths in the material of the iron target in the energy range from 150 to 600 keV at the angle to the normal from 0° to 65° is performed. The range of energies and irradiation angles for the hydrogen and helium ions are determined for the implantation into the radiation-induced defect-formation zone.     

Generation of electron nanobunches and short-wavelength radiation upon reflection of a relativistic-intensity laser pulse from a finite-size target

We have proposed an efficient scheme of generation of short dense electron bunches during the interaction at large angles of incidence of a laser pulse with a thin transversally semibounded laser target. Streams of bunches can be used to simultaneously and independently generate pulsed X-ray radiation as fast electrons hit secondary targets. Dependences of bunch parameters (the number of particles in the bunch and the bunch energy and thickness) on the angle of incidence and laser intensity have been obtained. It has been shown that, upon reflection from the target, the relativistic-intensity laser wave is efficiently converted (the energy-conversion factor reaches ～20%) into a sequence of electromagnetic tens-of-nanometer-long atto pulses, which follow one after another in the period of the initial laser wave. We have investigated how the parameters of the atto pulse depend on the angle of incidence and the laser intensity. We have shown that atto pulses are generated most efficiently at large angles of incidence (≥50°) of the laser pulse on the target.     

对重丰中子核区合成新核素的思考

分析了Ａ＞１７０质量区丰中子核素的产生、分离和鉴别过程,总结了在这一质量区用较轻中能重离子炮弹打重靶产生新核素的优点．提出了在在线同位素分离器上使用带有优良元素选择性的激光离子源和多层靶加气体传输系统的改进措施． The production, and process of separation and identification of new neutron rich nuclei with mass number A>170 were analyzed. The advantages of producing new isotopes in this mass region by lighter heavy particles on heavy targets were summarized. It is put forward an improvement method that a laser ion source and multilayer target combining with gas jet transport method can be used on on line isotope separator.     

Sputter damage in Si surface by low energy Ar+ ion bombardment

The damage distributions in Si(1 0 0) surface after 1.0 and 0.5 keV Ar⁺ ion bombardment were studied using MEIS and Molecular dynamic (MD) simulation. The primary Ar⁺ ion beam direction was varied from surface normal to glancing angle. The MEIS results show that the damage thickness in 1.0 keV Ar ion bombardment is reduced from about 7.7 nm at surface normal incidence to 1.3 nm at the incident angle of 80°. However, the damage thickness in 0.5 keV Ar ion bombardment is reduced from 5.1 nm at surface normal incidence to 0.5 nm at the incident angle of 80°. The maximum atomic concentration of implanted Ar atoms after 1 keV ion bombardment is about 10.5 at% at the depth of 2.5 nm at surface normal incidence and about 2.0 at% at the depth of 1.2 nm at the incident angle of 80°. However, after 0.5 keV ion bombardments, it is 8.0 at% at the depth of 2.0 nm for surface normal incidence and the in-depth Ar distribution cannot be observable at the incident angle of 80°. MD simulation reproduced the damage distribution quantitatively.     

Dynamic properties of the two-dimensional density-driven segregation

We discuss some dynamic properties of the segregation in vertically vibrated binary granular mixtures with the same size. We present a method that can accurately calculate the order parameter in the simulation. By use of the time evolution of the order parameter, we have found that the convergence of the segregated state depends at least on the vibration amplitude, the total mass of the particles, and also the density difference between the lighter and heavier particles.The convergence is quicker for larger vibration amplitude, lighter total mass of the particles and more density difference between the lighter and heavier particles. We have also found that thefluctuation is larger even after the steady state is reached for lighter total mass of the particles and less density difference between the lighter and heavier particles.     

Single element mapping in radiography

This article reports on the application of element‐specific mapping using the Bremsstrahlung of a commercial broad spectrum X‐ray source to map lighter elements (zirconium to tin) and heavier elements (tantalum to bismuth) individually within an image field. Grey level or image brightness has been obtained as a function of acceleration potential over a range of 15–75 kV for lighter elements and 55–150 kV for heavier elements at 1 kV intervals. Tikhonov regularisation was applied to the experimental grey level functions, using a model of the spectrum, to enhance spectral features associated with elemental K‐edges. These features were then used to test for a specific element at all points within an X‐ray image in order to map its presence over the whole image field. Hence it has been shown that it is possible to map specific target elements within an image, provided the grey level function over an appropriate energy range is known at all points. Copyright © 2009 John Wiley & Sons, Ltd.     

Messung der Eindringtiefe von Elektronen und Ionen in dünnen Aufdampfschichten

The penetration depth of electrons, H⁺-, He⁺-, Ne⁺-, and Ar⁺-ions in thin evaporated layers of alkali fluorides and alkaline earth fluorides has been investigated by measuring the excitation and deterioration of the luminescence caused by the bombardement with electrons and ions. Particle energy ranged up to 10 keV for electrons and the lighter ions and up to 30keV for the heavier ions; film thicknesses were chosen between 5 and 100μg/cm². The penetration depths defined by the two different techniques are called “maximum excitation depth” and “maximum deterioration depth”. By measuring the excitation depth a depth distribution may be obtained. Using the Bethe-equation a numerical penetration depth-energy-relation for electrons was derived which gives good agreement with the experimental values. The results of the deterioration depths of the ions are compared with the theoretical predictions ofLindhard andScharff.     

Calculation of LET-spectra of heavy cosmic ray nuclei at various absorber depths

The calculation is based on a factorization of fragmentation cross-sections into a projectile-depending and a target-depending part, which was found at Bavalac for high energy C and O ions. With this the known cross-sections for the fragmentation of heavy ions in collision with protons can be extrapolated to heavier targets. Considering the fragmentation and the energy loss of heavy nuclei the energy spectra of individual elements are calculated for different depths of absorber. This energy spectra can easily be converted to LET (linear energy transfer) spectra. The changes of the isotopic composition with absorber depth and its influence on the shape of the LET-spectra are discussed. The calculated results are compared with experimental data.     

基于多角度偏振差值曲线的目标识别初探

多角度偏振遥感在目标识别和地物观测中具有广阔的应用前景.从目标地物的偏振探测机理出发,讨论了它们偏振反射光谱的空间特征,以及由反射光的垂直振动分量和平行振动分量构成的偏振差值曲线的变化规律.结果显示:反射光的垂直振动分量与平行振动分量之差R⊥//随着折射率的变化而不同,且均在入射角80°附近达到最大;随着折射率的增加,...     

Minimization of the Total Depth of Internal Saw-Tooth Reliefs of a Two-Layer Relief-Phase Diffraction Microstructure

Results of studying the possibility to decrease the total depth of reliefs of a two-layer microstructure having two internal saw-tooth microreliefs reducing the dependence of the diffraction efficiency of the microstructure on the radiation wavelength and angle of radiation incidence on the microstructure are presented. These results allow one to minimize the complexity of obtaining optimum microrelief depths depending on requirements applicable to the diffraction optical element in the framework of the electromagnetic-diffraction theory. Optimum depths provide in the specified spectral range and interval of angles of radiation incidence the maximum possible (for the chosen width of the narrowest zone of the saw-tooth microrelief) value of the diffraction efficiency at the point of its minimum.     

同位旋依赖的碎块判断方法对重离子碰撞观测量的影响(英文)

该工作提出了一个同位旋依赖碎块判断方法用以描述重离子碰撞过程中的碎块形成。利用该方法可以改善输运理论对于核子以及轻带电粒子产额的描写,其在计算中降低了发射核子产额、增加碎块(特别是丰中子碎块) 的产额。对于丰中子轻带电粒子的增强主要出现在中心快度区。研究表明,该方法对于同位旋敏感的观测量,如,n/p,t/3He,Rmidyield 和isoscaling parameters 等,以及系统的平衡度的量度都会产生影响。We introduce isospin dependence in the cluster recognition algorithms used in the Quantum Molecular Dynamics model to describe fragment formation in heavy ion collisions. This change reduces the yields of emitted nucleons and enhances the yields of fragments, especially for heavier fragments. The enhancement of neutron-rich lighter fragments mainly occurs at mid-rapidity. Consequently, isospin dependent observables, such as isotope distributions, yield ratios of n/p,t/3He, Rmid yield and isoscaling parameters are affected. We also investigate how equilibration in heavy ion collisions is affected by this change.     

金属光栅表面增强喇曼散射TE模的计算分析

以纳米量级金属履带矩形光栅为模型,研究了表面增强喇曼散射的特性.针对TE模的入射光,采用耦合波原理对金属表面的衍射场进行了讨论,并用数值计算方法讨论了光栅周期、光栅深度等参量对表面增强的影响以及增强因子随第一级瑞利系数的变化关系.结果表明：在入射光波长为700 nm、光栅周期p=400 nm、 光栅深度d=150 nm、占空比为1/3、入射角度为10°时,获得最大增强,增强因子G可达102.     

亚微米光栅型导光板设计

提出了利用亚微米光栅制作导光板的方法,给出亚微米光栅型导光板的初始结构.用严格耦合波理论计算分析了在满足基底全反射条件的45°入射角下红(700 nm)、绿(555 nm)、蓝(465 nm)三色光垂直出射的亚微米光栅(0.651μm、0.516μm、0.433μm)在槽深0.05~0.9μm之间变化时,透射衍射效率在2%~43%之间变化.分析了亚微米光栅的作用,做出性能评价,并研究了特定范围入射角引起的衍射角变化.     

Photoelectron escape from iron oxide

Iron oxide of nanometer thickness were grown in situ by step-by-step oxidation of an iron foil to measure the escape probabilities of O 1s photoelectrons as a function of depth of origin, the so-called emission depth distribution function (EDDF), and the mean escape depth (MED). To record photoelectron spectra for a wide range of emission angles, the X-ray excitation source was positioned on the opposite side of the iron foil with respect to the analyzer. To excite photoelectrons on the side of the foil surface adjacent to the analyzer, the foil was made thin enough to be semitransparent to the X-ray radiation. The O 1s spectra were recorded for a wide range of oxide thicknesses until no features of metallic iron were recognized in the photoelectron spectra. The escape probability of the O 1s photoelectrons in the iron oxide was derived from the oxide-thickness dependence of the O 1s peak areas. The resulting EDDF reached a maximum beneath the oxide surface for X-ray incidence and electron-emission angles located along the surface normal. For the same incidence angle and an emission angle of 60°, the escape probability could be well approximated by a simple exponential function. The mean escape depths were obtained for both experimental geometries and agreed well with the available theory.     

Neutron productions in the fragmentation of relativistic heavy nuclei and formation of a beam of high-energy neutrons

The production of quasimonoenergetic high-energy neutrons at zero angle (0°) in the spallation of relativistic heavy nuclei is discussed by considering the example of the interaction of lead nuclei with light target nuclei. It is shown that this process can be used to generate a beam of high-energy neutrons at existing heavy ion accelerators. At the same time, itmay lead to the appearance of a parasitic neutron beam because of the interaction of the heavy-ion beam used with beam line and experimental setup materials.     

赫兹型微裂纹光场调制增强作用的系统研究

通过改变裂纹的倾角、宽度和深度参数,模拟了赫兹型裂纹在不同参数下对光场调制能力的不同. 模拟发现,倾斜角度为20.9°到45°之间的裂纹危害最大,倾角大于45°小于48.2°的裂纹危害也十分大,而倾斜角度为45°时的裂纹危害最小. 对于30°倾角的赫兹型裂纹,一定范围内,赫兹型裂纹深度的增加会导致其光场调制增强能力呈二次方关系增加,但宽度的增加不会使其光场调制增强作用增加. 裂纹深度和宽度的增加可以用来近似裂纹的演化过程,所以裂纹的扩展导致了其光场调制能力的增加,进而导致损伤增长速率的加快,这和e指数损伤增长规律相符. 关键词： 损伤增长 亚表面缺陷 赫兹型裂纹 光场增强     

Study of the sensitivity of size-averaged scattering matrix elements of nonspherical particles to changes in shape, porosity and refractive index

Studies of the physical parameters that influence the single scattering properties of a size distribution of small particles in random orientation are fundamental in understanding the origin of the observed dependence of the scattering matrix elements on the scattering angle. We present results of extensive calculations of the single scattering matrices of small nonspherical particles performed by a computational model based on the Discrete-Dipole Approximation. We have particularly studied the sensitivity of the size-averaged scattering properties at visible wavelengths of nonspherical, randomly oriented absorbing particles considering changes in shape, porosity and refractive index. These studies have importance regarding the inversion of physical properties of small particles as measured in the laboratory and the dust properties in various astrophysical and atmospherical environments. We have found that size distributions of randomly oriented irregular particles of different shape, including large aspect ratio particles, show similar scattering matrix elements as a function of the scattering angle, in contrast with the pattern found for regularly shaped particles of varying axis ratios, for which the scattering matrix elements as a function of the scattering angle show much larger differences among them. Regarding porosity, we have found a very different pattern in the scattering matrix elements for an ensemble of compact and porous particles. In particular, the linear polarization for incident unpolarized light produced by compact and absorbing particles of large size parameter tend to mimic the pattern found for large absorbing spheres. For porous particles, however, the linear polarization for incident unpolarized light tends to decrease as the size of the particle grows, with the maximum being displaced towards smaller and smaller scattering angles.     

Zur Lage des Maximums der Ausbeutekurve bei der Sekundärelektronenemission

There exists a quantitative connection between penetration depth of primary electrons, the maximum escape depth of secondary electrons and the position of the maximum of the yield curve if one assumes: (1) the maximum of the yield curve is determined by an energyE _p ^max of the primary electrons where the maximum penetration depth of primary electrons equals the maximum escape depth of the secondary electrons; and (2) the maximum escape depth of secondary electrons is given by 10 atomic layers for all metals investigated as it has been found earlier by Mayer and Hölzl for potassium. These assumptions are confirmed experimentally by measurements of yield curves and energy distributions at defined conditions and by variation of several parameters as temperature, contamination of the surface, surface roughness, evaporation conditions, and angle of incidence of the primary electrons.     

合金钢材料光学常数的椭偏测量及其修正

用椭偏法测量了入射光波长0.632μm、入射角50°至85°时某合金钢的光学常数。考虑材料表面的粗糙度,用Ohlidal-Lukes理论对所测光学常数值进行修正,发现椭偏参量的修正量随入射角增大而增大。结果表明,用椭偏法测量合金钢光学常数时采用较小入射角能获得更精确的样片光学常数。     

Separation of an isotope as a precursor of a gamma-raylaser medium

The nuclear isomer ¹⁷⁸Hf^m2, expected to be the most promising candidate for the gamma-ray medium, is rather difficult to produce in large quantities. There are a few ways to create this isomer, such as the irradiation of ¹⁷⁹Hf with high-energy neutrons through the (n,2n) reaction, the irradiation of ¹⁷⁶Yb with high-energy α particles through the (α,2n) reaction, the irradiation of ¹⁸¹Ta with protons through the (p,2p2n) reaction. In some of these reaction schemes the isotopically pure target works better than the natural one from the viewpoint of spectroscopic purity, handling of radioactive materials and productivity. However, isotope separation of heavy elements for producing a precursor as a target material is difficult in terms of cost/effectiveness. The atomic vapor laser isotope separation (AVLIS) method is expected as the most efficient way compared with the normal electromagnetic separation method. This revised version was published online in August 2006 with corrections to the Cover Date.