利用同步辐射形貌术研究晶体缺陷的实验方法探讨

利用同步辐射X射线形貌术研究晶体缺陷,是近年来发展起来的一种优良的实验方法,本文在研究LNP等晶体缺陷的同时,对这种实验方法进行了系统的探讨,讨论了散射光的消除,焦距的选择,样品的透明度与厚度,曝光的时间,底片的冲洗等问题,以及在缺陷研究中对晶体衍射的劳厄斑点的选取依据。     

邻苯二甲酸氢钾(KAP)的同步辐射截面形貌术

本文叙述邻苯二甲酸氢钾(KAP)晶体内部不完整性(滑移位错等)的同步辐射截面形貌图的衬度研究工作。有关缺陷象衬度随波长增加而提高的实验事实同引用均匀畸变动力学的理论所引入的平均应变梯度参数β和βt_eff的理论计算结果,相当符合,它为应用同步辐射源来清晰显示单晶中有关缺陷,提供一个波长选择的依据。 关键词：     

KTP(001)晶体分光性能研究

根据同步辐射光源对软X射线分光晶体的性能要求,分析了软X射线能区常用分光晶体的性能优劣,指出对于晶格常数值大的分光晶体,KTP(KTiOPO₄)(011)是该能区比较理想的分光晶体. 同时提出了一种利用同步辐射光源测量晶体衍射效率的实验方法,指出光源的发散度与晶体的衍射效率密切相关. 测量了KTP(011)晶体的晶格常数,给出了KTP(011)晶体的实测衍射效率. 关键词： 同步辐射 KTP(011)晶体 衍射效率 光源发散度     

Light Source for Synchrotron Radiation X-Ray Topography Study at Beijing Syncrotron Radiation Laboratory (BSRL)

Characteristics of the synchrotron radiation source for X-ray topography study at Beijing Synchrotron Radiation Laboratory (BSRL) is desribed in this paper,local geometrical resolution of topographs is discussed,the diffracting intensities of white beam topography is given.     

Numerical simulation of energy relaxation processes in a ZnMoO<Subscript>4</Subscript> single crystal

We present the results of our experimental investigation and numerical simulation of excitation-energy relaxation processes in zinc molybdate crystals. We show that our kinetic model of the energy relaxation makes it possible to describe basic features of experimental results. Using this model, we estimate the trap concentration in ZnMoO₄ upon irradiation of the crystal by VUV synchrotron radiation and X-ray radiation. We conclude that prolonged phosphorescence of ZnMoO₄ that is observed after irradiation of the crystal by X-ray radiation can be caused by the occurrence of additional traps with a low activation energy.     

On the theory of radiation of an infinitely long charged current-carrying thread in a uniaxial transparent crystal

The problem relating to the synchrotron radiation of a charged current-carrying thread in a uniaxial transparent crystal is considered here using the Sitenko-Kolomensky method. The formulas for the intensity of the synchrotron radiation and the limiting values of the formulas giving the intensity of the Cerenkov radiation of a thread moving uniformly and rectilinearly parallel to the optical axis of a crystal have been derived.     

Fluorescence decay time measurements in tetracene crystals excited with synchrotron radiation

Fluorescence decay times from tetracene single crystals excited at room temperature with synchrotron radiation have been recorded as a function of the excitation wavelength (in the 400–500 nm range). A non-exponential decay with two decay rates is observed. The analysis of our data shows that the first singlet exciton level of tetracene (single crystal) decays radiatively mainly through, as we call it, channel 1, with a lifetime of 0.200 ± 0.020 ns. About 10% of the emitted fluorescence transits through channel 2 with a lifetime of 1.7 ± 0.2 ns. These results do not agree with previously published decay data obtained when tetracene is excited by means of powerful lasers. Thus there is experimental evidence to believe that the decay properties of condensed materials can be very dependent on the excitation density. Because synchrotron radiation compared to lasers is a very weak source, and therefore secondary effects are minimized in our experimental conditions, the decay values reported in the present work are the true lifetimes of the tetracene single crystal.     

Radiation from a charged current-carrying filament in a transparent uniaxial crystal

The problem of Vavilov-Serenkov (Cherenkov) and synchrotron radiation from a charged current-carrying filament in a transparent uniaxial crystal is considered. Formulas are obtained for the spectral distribution of the radiated intensity. The limiting transition of the equations for the spectral intensity distribution of synchrotron radiation into the corresponding formulas for Vavilov-Serenkov radiation is considered.     

Synchrotron radiation refraction topography for characterization of lightweight materials

The employment of synchrotron radiation for refraction topography of materials has considerable advantages over standard x‐ray sources. The much higher beam intensity and the parallel and monochromatic radiation provide faster measurements and better angular and spatial resolution. X‐ray refraction techniques image the inner surface and interface concentration of micro‐structured materials. This effect of x‐ray optics is additional to small‐angle scattering by diffraction, when the scattering objects reach micrometre dimensions. We have developed x‐ray refraction techniques within the last decade in order to meet the growing demands for improved non‐destructive characterization of high‐performance composites, ceramics and other low‐density materials. Sub‐micron particle dimensions, the pore size of ceramics, the crack density distribution and single fibre debonding within damaged composites can be measured and visualized by computer‐generated interface topographs. For this purpose investigations are now being performed at the new hard x‐ray beamline of the Federal Institute for Materials Research and Testing (BAM) at BESSY, Berlin. This BAMline provides monochromatic radiation of photon energies from 5 to 60 keV from a double multilayer and/or a double‐crystal monochromator. A separate instrument is dedicated to the further development and application of synchrotron radiation refraction (SRR) topography. Different from conventional small‐angle scattering cameras with collimating slits and pinholes, scattering angles down to a few seconds of arc are selected by a single‐crystal analyser, similar to a Bonse–Hart diffractometer. A 20 µm spatial resolution of the scattering micro‐structures is achieved by a CCD camera with a fluorescent converter. First SRR topographs of aircraft composites [carbon fibre‐reinforced plastics (CFRP), carbon fibre‐reinforced ceramics (C/C), metal matrix ceramics (MMC)] will be reported. Copyright © 2004 John Wiley & Sons, Ltd.     

Synchrotron radiation of crystallized beams

We study the modifications of synchrotron radiation of charges in a storage ring as they are cooled. The pair correlation lengths between the charges are manifest in the synchrotron radiation and coherence effects exist for wavelengths longer than the coherence lengths between the charges. Therefore, the synchrotron radiation can be used as a diagnostic tool to determine the state (gas, liquid, crystal) of the charged plasma in the storage ring. We show also that the total power of the synchrotron radiation is significantly reduced for crystallized beams, both coasting and bunched. This opens the possibility of accelerating particles to ultrarelativistic energies using small-sized cyclic accelerators.     

X-ray transition radiation of electrons with energy of 300 to 900 MeV in periodic multifoil radiators

Results of experiments conducted at the Tomsk synchrotron to study resonant X-ray transition radiation generated by relativistic electrons in periodic multifoil radiators are reviewed. Both the internal synchrotron beam and the external secondary electron beam from the pair magnetic γ-spectrometer with energies ranging from 300 to 900 MeV were used in the experiments. The radiators consisted of many thin amorphous foils of various materials. The generation of X-ray radiation in a compound radiator consisting of a multifoil radiator and a crystal is also studied. In this case, the resonant X-ray transition radiation generated in the multifoil radiator is diffracted in the crystal and emitted at Bragg angles, together with the parametric X-ray radiation generated in the crystal. Spectral and angular properties of the resonant X-ray transition radiation and diffracted resonant X-ray transition radiation are investigated. The ratio between the contributions from the diffracted resonant X-ray transition radiation and other types of radiation to the total coherent X-ray radiation flux generated by electrons in periodic structures and crystals is estimated.     

The influence of defects in the crystal structure on helium diffusion in quartz

The solubility and diffusion of helium in quartz crystals are investigated as functions of the distribution and density of structural defects. The types of defects in the crystals are identified and their distribution over growth sectors is determined by x-ray diffraction topography and phase radiography with a synchrotron radiation source. The effective solubility and effective diffusion coefficients for helium in quartz are estimated from the experimental data on the amount of helium extracted from samples with different contents of defects. It is revealed that the effective diffusion coefficient of helium depends on the number of dislocations.     

Highlights of synchrotron radiation

The applications of the electromagnetic radiation generated by relativistic electrons circulating in synchrotrons and storage rings have rapidly extended into many scientific disciplines. This article first briefly reviews the history of synchrotron radiation, and recapitulates its properties. The available sources are listed, and some aspects of the facilities that are required to make use of the radiation are discussed, with particular emphasis on the optical elements. Several noteworthy examples of scientific research conducted with synchrotron radiation are described. These are drawn principally from the X-ray region, and comprise X-ray fluorescence, small-angle scattering, powder profile refinement, extended X-ray absorption fine structure, topography, time-resolved spectroscopy, and VUV and photoelectron spectroscopy of solids. In conclusion, a few topics are mentioned relating to the future expansion and application of synchrotron radiation research facilities.     

Contrast analysis of Shockley partial dislocations in 4H-SiC observed by synchrotron Berg–Barrett X-ray topography

Shockley partial dislocations in 4H-SiC were observed using monochromatic synchrotron X-ray topography with a grazing-incidence Bragg-case geometry, that is, Berg–Barrett topography. The contrast of partial dislocations at the edges of Shockley-type stacking faults is discussed in terms of whether they have C- or Si-core edge components, or screw components. The dissociated state of basal-plane dislocation is discussed on a basis of the stacking sequence for basal-planes in the 4H-SiC crystal structure. It is expected that the results obtained in this study will be useful for characterizing Shockley-type stacking faults in Berg–Barrett topography.     

Spin polarized energy-resolved photoemission from Ni(111) using synchrotron radiation

We report on the first energy-resolved (retarding field mode) spin polarized photoemission measurement from a Ni(111) single crystal using synchrotron radiation from the ACO storage ring at LURE(ORSAY) It is shown that exchange effects can be detected for electron states well below the Fermi energy and that spin polarized, constant-initial-state spectroscopy of ferromagnets using synchrotron radiation is feasible.     

Coplanar three-beam X-ray diffraction study in TeO<Subscript>2</Subscript> single crystal using synchrotron radiation

The results of the first experimental study of coplanar three-beam X-ray diffraction in a paratellurite (TeO₂) single crystal using synchrotron radiation on a Kurchatov synchrotron radiation source are presented. Four cases with (220, 371), (220, 464), (220, 370), and (110, 557) indices have been investigated. In all cases the change of the rocking curve shape of the weak reflection has been observed due to the multibeam interaction resulting in the appearance of two peaks in the reflection curve corresponding to two scattering mechanisms: amplitude and resonance. The origin of the insufficient resolution in the experiments has been considered. It has been shown that the obtained data correspond to the results of the computer simulation.     

同步辐射与GGG：Nd^3＋晶体的相互作用

用北京同步辐射489A-VUV束线作为连续光源测定了GGG:Nd~(3+)晶体的短波吸收光谱。用束线4B9A-WX作为光源激发GGG:Nd~(3+),测定了它的XEOL(X-ray excited optical luminescence)。     

Observation of magnetic domain wall movements by X-ray topography using synchrotron radiation

Antiferromagnetic domain wall movements in KNiF₃ have been observed directly by X-ray topography using synchrotron radiation. Topographs were taken in fields up to 1.3 T at a temperature of 77 K. In contrast to X-ray topography using conventional sources, the apparatus is simple and it is possible to obtain good resolution topographs despite the geometrical limitations imposed by the cryostat and electromagnet. Exposure times were typically 8 seconds when recording on Ilford L4 Nuclear Emulsion plates.     

Radiation defect clustering in graphite studied by synchrotron radiation scattering

The formation of radiation defect clusters as interstitial dislocation loops in pyrographite irradiated by 20-MeV carbon ions in a cyclotron has been studied by means of synchrotron radiation scattering. The experimental data are interpreted in terms of the Krivoglaz model and the model of deformation domain formation by dislocation loops. Parameters of the pyrographite crystal lattice in the deformed state upon ion irradiation have been determined using experimental data on the shift and broadening of the Bragg peaks. The results of experiments and their theoretical analysis indicate that the phenomena of the crystal lattice densification (shrinkage) and the radiation-induced swelling (increase in volume) observed for graphite irradiated by fast neutrons in a nuclear reactor can be studied in model experiments on charged particle accelerators using irradiation of the samples with carbon ions at much lower doses and significantly shorter exposure times.     

High pressure x-ray diffraction techniques with synchrotron radiation

This article summarizes the developments of experimental techniques for high pressure x-ray diffraction(XRD) in diamond anvil cells(DACs) using synchrotron radiation. Basic principles and experimental methods for various diffraction geometry are described, including powder diffraction, single crystal diffraction, radial diffraction, as well as coupling with laser heating system. Resolution in d-spacing of different diffraction modes is discussed. More recent progress, such as extended application of single crystal diffraction for measurements of multigrain and electron density distribution, timeresolved diffraction with dynamic DAC and development of modulated heating techniques are briefly introduced. The current status of the high pressure beamline at BSRF(Beijing Synchrotron Radiation Facility) and some results are also presented.