Ab initio simulation of resonant forbidden reflections in Ge crystals

Forbidden reflections are observed in the case of diffraction of synchrotron radiation with wave-lengths close to the absorption edges in crystals. A new method for calculating the intensity of thermal-motion-induced (TMI) forbidden reflections is proposed in this paper. It includes two stages: simulation of instantaneous thermal atomic displacements using ab initio molecular dynamics and subsequent quantum-mechanical calculations of the resonance scattering amplitude for various configurations. This procedure is used to calculate the temperature dependence of the 600 reflection intensity for Ge. The proposed method for simulating forbidden TMI reflections is suitable for any crystal structures and can explain many results so far obtained using synchrotron.     

Determination of spatial temperature distributions in a laminar premixed ethylene/air flame by laser-induced atomic fluorescence

A quick and simple detection system for spatially resolved temperature measurements in flames based on laser-induced thermally assisted atomic line fluorescence of seeded rubidium atoms is described. The fluorescence light from two atomic states is dispersed and simultaneously recorded by a CCD camera. The fluorescence ratio distributions lead directly to absolute temperature distributions. The practical use, the spatial and temperature resolution and error limits of the method are discussed and compared with other procedures for temperature measurements.     

Optimal x-ray beam formation using a focusing mirror at the Langmuir synchrotron station

A beam focusing method is proposed for the Langmuir station of the Kurchatov synchrotron radiation source. This method can be implemented during experiments on recording the fluorescence yield intensity as a function of the angle between an incident beam and a sample surface. The x-ray beam is focused by a cylindrical mirror in such a way that the dimensions of the spot illuminated by the beam on a Langmuir film remain within the input angular aperture of an energy dispersive detector during scanning in the angle of incidence. The relationships for calculating the dimension of the illuminated spot in the scattering plane and the angular divergence of the focused x-ray beam are derived taking into account the dimension of the synchrotron radiation source and spherical aberration. Recommendations for optimizing station parameters and experimental conditions are presented.     

Advances in the measurements of the mass attenuation coefficients

The knowledge of atomic fundamental parameters, such as mass attenuation coefficients or fluorescence yields with low uncertainties, is of decisive importance in elemental quantification involving X-ray fluorescence analysis techniques. Several databases providing the mass attenuation coefficients are accessible and frequently used within a large community of users. These compilations are most often in good agreement for photon energies in the hard X-ray ranges. However, they significantly differ for low photon energies and around the absorption edges of the elements. Mass attenuation coefficients of several elements were determined experimentally in the photon energy range from 100 eV to 35 keV by using monochromatized radiation at the SOLEIL synchrotron (France). The application of high-accuracy experimental techniques resulted in low uncertainty mass attenuation coefficients. The results are compared with tabulated data.     

大气颗粒物重金属元素分析技术研究进展

大气颗粒物已经成为当前大气环境首要污染物,而其中重金属由于具有非降解性和滞后性,严重威胁人类生命和自然环境,已成为当前研究热点。对分析大气颗粒物中重金属元素所用原子吸收光谱法、电感耦合等离子体原子发射光谱法、电感耦合等离子体质谱法、荧光光谱法、中子活化法、辉光放电原子发射光谱法、微波等离子体原子发射光谱法和激光诱导击穿光谱法进行了综述,并尝试对这些技术的不足之处提出一些改进建议：连续光源原子吸收光谱法同时测定多种元素,原子发射光谱法直接测定颗粒物,高分辨率激光剥蚀电感耦合等离子质谱法测定固体样品,低散射同步加速荧光法测定大气颗粒物和k₀中子活化法测定对流层发射性元素。大气颗粒物重金属元素的时空分布差异和人类对环境空气质量要求的提高以及现代仪器科学技术的高速发展促使大气颗粒物重金属元素分析技术朝着实时、快速、检出限低、直接测定和操作简便的方向发展。     

蒸气发生-原子荧光光谱法测定中草药中不同形态的汞

建立了蒸气发生-原子荧光光谱法测定中草药复方方剂原生药、残渣、悬浮态、可溶态的无机汞和有机汞的方法。研究了仪器的工作条件、试剂浓度、增感剂对汞原子荧光强度的影响及有机汞的氧化条件,探讨了共存离子对汞测定的干扰和消除方法,利用本方法成功地对万氏牛黄清心方剂中的汞进行了形态分析。方法检出限为7.6 ng·L-1,RSD为1.56%～3.28%,回收率为90.3%～110.3%。     

空心阴极灯激发的微波等离子体炬原子/离子荧光光谱研究--钙的原子/离子荧光光谱

用强短脉冲供电技术的空心阴极灯作激发源、微波等离子体炬作原子／离子化器，建立了原子／离子荧光光谱实验装置。详细研究了微波等离子体功率、观察高度、空心阴极灯电流等因素对原子／离子荧光信号强度的影响，测量了系统对Ca的原子／离子荧光光谱的检出限。     

同步辐射X射线荧光光谱国内外研究进展

同步辐射光源是带电粒子在加速器储存环中以接近光速的速度运动时,沿轨道切线方向发射出的辐射,同步辐射X射线荧光分析(SR-XRF)是以同步辐射X射线作为激发光源的X荧光光谱分析技术.同步辐射X射线荧光分析包括了用于微区及微量元素分析的同步辐射XRF、用于表面及薄膜分析的同步辐射全反射X射线荧光(SR-TXRF)以及用于三...     

Resonance fluorescence excited by macroscopic superposition in a seedback soop

The resonance fluorescence of an individual atom excited by an optical field in a Yurke-Stoler state, consisting of a superposition of two coherent states with opposite phase, is studied. It is proposed that the decoherence of the field state be eliminated by means of electrooptic feedback [Phys. Rev. Lett. 78, 840 (1997)]. The master equation for the density operator of the atom-field system is derived and an analytic solution is obtained for the case where the change in the field is adiabatically slow. It is shown that the interaction entangles the atomic and field states. A new effect is predicted: there are no Rabi oscillations of the dipole moment and of the atomic populations with the excitation method described.     

Theoretical study of exafs-like modulation observed in graphite 2scis spectra

The EXAFS-like oscillation observed during graphite C 2s constant-initial-state (CIS) spectroscopy using a synchrotron radiation source is analyzed within the theoretical treatment previously proposed by the authors. The interference between the electron waves emanating from different atomic sites plays an important role in the phenomenon.     

"Devil's staircase"-type phase transition in NaV2O5 under high pressure

The "devil's staircase"-type phase transition in the quarter-filled spin-ladder compound NaV2O5 has been discovered at low temperature and high pressure by synchrotron radiation x-ray diffraction. A large number of transitions are found to successively take place among higher-order commensurate phases with 2a x 2b x zc type superstructures. The observed temperature and pressure dependence of modulation wave number q(c), defined by 1/z, is well reproduced by the axial next nearest neighbor Ising model. The q(c) is suggested to reflect atomic displacements presumably coupled with charge ordering in this system.     

空间辐射地面模拟装置(SESRI)同步加速器注入设计和模拟研究

国家"十二五"工程将在哈尔滨工业大学建造一台空间辐射地面模拟装置（SESRI）,该装置能够模拟空间辐照环境,对研究离子辐照材料、生命体等具有重要意义。SESRI主要由双ECR离子源,直线注入器,同步环和3个高能实验终端组成。周长为43.9 m的同步环作为装置的核心部分,能够向3个实验终端输送离子种类多、能量范围广的粒子束。为了保证环内有足够的粒子数,注入系统的设计至关重要,SESRI同步环采用多圈注入方案,并利用ACCSIM程序模拟粒子真实运动情况。结果表明,粒子的注入效率为85.5%,离子数增益可达17.1,可满足设计要求。Space Environment Simulation and Research Infrastructure (SESRI), which is one of the large-scale scientific projects proposed in National Twelfth Five-Year Plan of China, will be constructed in Harbin Institution of Technology. The SESRI project dedicated to space radiation consists of two ECR ion sources, a high intensity ion linac, a synchrotron and 3 research terminals. As the key part of the complex, a 43.9 m synchrotron can provide broadest energy range and variable ion beam for each terminal. To obtain required intensity in the synchrotron, the injection system is significant. A multi-turn injection scheme is adopted in the synchrotron and the injection process is simulated by ACCSIM with multi-particle tracking method. The results show that the injection efficiency and intensity gain factor can reach 85.5% and 17.1 respectively. The multi-turn injection system can meet the design requirement.     

ARDESIA: A fast silicon drift detector X-ray spectrometer for synchrotron applications

ARDESIA, a four-channel X-ray spectrometer based on silicon drift detectors (SDDs), is presented. It has been developed for synchrotron applications targeting especially X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) with good energy resolution at high count rates (a few Mcps per second). The main target applications are XRF and XAFS techniques. The system features a 2 × 2 monolithic array of 5-mm-pitch SDDs cooled with a double Peltier scheme and coupled to a four-channel CUBE charge preamplifier. Different digital pulse processors allowing operation in Mcps per second count rates are employed. The results of preliminary characterization measurements performed at both the LNF DAΦNE-Light DXR1 beamline and the ESRF LISA BM-08 are reported, in particular, XRF measurements on low atomic number elements (down to the Carbon K-line, 270 eV) and extended X-ray absorption fine structure of trace materials in pyrite.     

原子荧光光谱法测定水性涂料中可溶性汞

应用原子荧光光谱法测定水性涂料中可溶性汞，对影响测定的参数进行了优化，汞的检出限为0.03ng/mL。     

冷原子荧光光谱法测定3种中药材中的痕量汞

采用硝酸-双氧水体系及高压消解法处理样品,建立了氢化物发生-冷原子荧光光谱法测定中药材中的痕量汞的测定方法,研究了仪器工作条件、介质酸及浓度、还原剂硼氢化钾浓度对测量结果的影响并进行了优化,在最佳实验条件下对3种云南产地中药材进行了测试,汞的校准曲线在0—10μg.L-1范围内线性良好,相关系数为0.9999,方法的检出限为2.9ng.L-1,RSD为1.8%,测定的3种中药材中的汞含量为5.62—17.29ng.-g 1,加标回收率为90.3%—105.2%。     

Investigation of nanoscale element distributions at surfaces with grazing incidence X‐ray spectroscopy techniques – an instrumentation study

Grazing incidence X‐ray methods are well‐established in the characterization of nanostructures at interfaces and surfaces. The purpose of the experiments reviewed in this work is the comparative characterization of different instrumentation concepts for grazing incidence X‐ray fluorescence analyses. Fluorescence scans recorded with a total reflection X‐ray fluorescence spectrometer featuring a variable angle of incidence are compared with data obtained with synchrotron radiation. The conclusions to the element distribution profiles, which are drawn from fluorescence scans carried out with the respective instrument, are compared. This way, the suitability of the total reflection X‐ray fluorescence spectrometer to complement synchrotron radiation facilities and the possibility to transfer surface and interface analyses from the synchrotron to the laboratory are assessed. The structures investigated include an Au on Si surfaces in the form of layers and particles, submicrometer‐sized droplets, a liquid film, and ions implanted into a Si wafer. Copyright © 2014 John Wiley & Sons, Ltd.     

X-ray pump optical probe cross-correlation study of GaAs

Ultrafast dynamics in atomic, molecular and condensed-matter systems are increasingly being studied using optical-pump, X-ray probe techniques where subpicosecond laser pulses excite the system and X-rays detect changes in absorption spectra and local atomic structure(1-3). New opportunities are appearing as a result of improved synchrotron capabilities and the advent of X-ray free-electron lasers(4,5). These source improvements also allow for the reverse measurement: X-ray pump followed by optical probe. We describe here how an X-ray pump beam transforms a thin GaAs specimen from a strong absorber into a nearly transparent window in less than 100 ps, for laser photon energies just above the bandgap. We find the opposite effect-X-ray induced optical opacity-for photon energies just below the bandgap. This raises interesting questions about the ultrafast many-body response of semiconductors to X-ray absorption, and provides a new approach for an X-ray/optical cross-correlator for synchrotron and X-ray free-electron laser applications.     

The formation of O(3s3S0) and N(3s4P) by photodissociation of NO

The dissociation of NO molecules to excited atomic states by dispersed synchrotron radiation (700 Å – 800 Å) is investigated by observing vuv-fluorescence (1050 Å – 1400 Å) of the fragments. The atomic levels are populated by predissociation of high-lying molecular states.