基于能量色散X射线荧光光谱的鱼粉产地溯源方法研究

鱼粉是一种在养殖业中占有重要地位的高蛋白饲料原料。我国对鱼粉的市场需求很大,但不同产地的鱼粉存在品质差异的问题。为保证鱼粉品质安全,建立鱼粉产地溯源系统具有非常重要的意义。能量色散X射线荧光光谱根据元素辐射X射线荧光光子能量不同,能够检测样品矿物质元素种类和含量。鱼粉所含矿物质元素种类和含量会因鱼粉产地不同而存在差异,因此提出采用能量色散X射线荧光光谱(EDXRF)法对鱼粉进行扫描检测来获得鱼粉的元素信息,将原始光谱进行预处理后,采用鲸鱼算法改进的自适应净信号权重局部超平面方法识别鱼粉样品的光谱向量,从而对其产地进行溯源判别。首先对产地来自辽宁和浙江的51份鱼粉样品进行压片,并在EDXRF谱仪的检测程序中设置不同的滤光片,得到51组(每组6条光谱)光谱。然后对光谱进行预处理,采用基于自适应迭代重加权惩罚最小二乘法算法（airPLS）进行基线校正,从而消除基线漂移的影响,提高精度。采用小波变换对光谱进行平滑,去除光谱曲线的高频噪声。选取每个鱼粉样品6条光谱的有效区段,计算谱峰面积,获得代表样品矿物质元素含量的16维向量。最后采取鲸鱼算法对自适应净信号权重局部超平面(ANWKH)方法的关键参数（近邻数、主成分数、调节参数）进行最优选择,再利用寻找到的最优参数建立自适应净信号权重局部超平面模型,随机选取每个产地鱼粉样品的70%作为训练集,30%作为测试集进行鱼粉产地判别。鱼粉样品分别来自辽宁和浙江两个产地,经预测模型识别正确率分别为94.3%和100%,总正确率为97.3%,均高于人工寻找参数的自适应净信号权重局部超平面分类准确率。结果表明,基于能量色散X射线荧光光谱的鱼粉溯源方法能够准确地实现鱼粉产地溯源,经鲸鱼算法改进后的自适应净信号权重局部超平面方法能够寻找到最优参数,建立分类准确度更高的模型,为以后进行更加详细的国内外鱼粉产地溯源提供了参考。     

Photoinduced absorption of THz radiation in semi-insulating GaAs crystal

The influence of optical illumination on transmission of THz radiation through a bulk crystal of semi-insulating GaAs is experimentally studied. It is established that, without additional illumination, absorption of electromagnetic waves with a frequency of about 1 THz in the studied crystal is almost absent. Optical illumination in the spectral range of fundamental absorption of the crystal does not affect the transmission of THz waves. At the same time, if the illumination photon energy is a little below the edge of fundamental absorption, i.e., actually in the transparency region, the transmission of THz radiation drops sharply. At liquid helium temperature, the maximum effect is achieved for the energy of optical photons lower by approximately 30 meV than the crystal band gap. Further shift of the illumination toward lower photon energies is accompanied by almost complete recovery of the transmission. With increasing sample temperature, the spectral range of efficient action of the illumination shifts together with the edge of fundamental absorption toward lower photon energies.     

K荧光辐射场MC模拟与能谱测量分析

K荧光辐射装置可填补国内超大型测量面积核辐射探测器计量检定需求,该装置具通量高、能量点多、单色性好、有成本低、即开即用等优势。其原理是X射线光机发射出的X射线轰击辐射体材料产生多种特征X射线即荧光射线,在荧光射线出射路径上加入次级过滤器吸收掉多余的射线以提高荧光纯度,辐射体以及次级过滤器的材料厚度值与荧光产额、纯度直接相关。通过MC(Monte Carlo)程序计算荧光装置各项指标参数结果,指导后期试验装置的建立和研究,MCNP5(Monte Carlo N Particle Transport Code)软件模拟Cs₂SO₄辐射体数据表明：荧光装置具有良好的屏蔽和准直的效果,荧光以辐射体中心垂直面呈对称逐渐减小分布;荧光产额随着辐射体厚度的增加逐渐增大,但存在相对饱和厚度值,即辐射体达到一定厚度值以后,荧光产额不再随辐射体厚度的增加而增大,而是趋于饱和状态;为获取单一能量荧光辐射场,在荧光出射束方向增加次级过滤器TeO₂材料,其吸收L,K_β射线会远远大于K_α射线,以达到消除L...     

Electronic excitations and luminescence of SrMgF4 single crystals

The electronic and crystal structures of SrMgF₄ single crystals grown by the Bridgman method have been investigated. The undoped SrMgF₄ single crystals have been studied using low-temperature (T = 10 K) time-resolved fluorescence optical and vacuum ultraviolet spectroscopy under selective excitation by synchrotron radiation (3.7–36.0 eV). Based on the measured reflectivity spectra and calculated spectra of the optical constants, the following parameters of the electronic structure have been determined for the first time: the minimum energy of interband transitions E _g = 12.55 eV, the position of the first exciton peak E _n = 1 = 11.37 eV, the position of the maximum of the “exciton” luminescence excitation band at 10.7 eV, and the position of the fundamental absorption edge at 10.3 eV. It has been found that photoluminescence excitation occurs predominantly in the region of the low-energy fundamental absorption edge of the crystal and that, at energies above E _g , the energy transfer from the matrix to luminescence centers is inefficient. The exciton migration is the main excitation channel of photoluminescence bands at 2.6–3.3 and 3.3–4.2 eV. The direct photoexcitation is characteristic of photoluminescence from defects at 1.8–2.6 and 4.2–5.5 eV.     

X射线荧光光谱中散射效应对荧光强度的贡献研究

采用理论计算和实验测定的方法研究了在纯元素样品、BaB二元样品及熔融片样品中三种散射效应对荧光强度的贡献(包括相干散射X射线激发的荧光强度、非相干散射X射线激发的荧光强度以及其他方向的一次荧光X射线被散射进探测方向的强度)大小及其变化规律。研究结果表明,三种散射效应对荧光强度的贡献大小与所研究元素原子特征谱线的能量及样品的基体有关,元素原子的特征谱线能量越高,散射效应对荧光强度的贡献越大;轻基体样品中散射效应对荧光的贡献比重基体样品大。实验证明,将散射效应包括在基本参数法的理论计算中可以有效地提高理论计算的准确度。     

Potential and restriction of high resolution,high energy photoemission in 400–8,000 eV for studying strongly correlated electron systems

InSe and InSe:Er single crystals were grown by using the Bridgman–Stockbarger method. The absorption measurements were carried out for voltage U=0 and U=30 V states of InSe and InSe:Er samples in the temperature range of 10–320 K with a step of 10 K. The absorption edge shifted towards longer wavelengths and the intensity of the absorption spectra decreased under a 5.90 kV/cm electric field. The same binding energy values for InSe and InSe:Er were calculated as 22.2 and 14.2 meV at U=0 and U=30 V, respectively. The steepness parameters and Urbach energies for InSe and InSe:Er samples increased with increasing sample temperature in the range of 10–320 K. An applied electric field caused a shift and a decrease of the intensity of the absorption spectra and an increase in the Urbach energy and steepness parameters. The shift of the absorption edge can be explained on the basis of the Franz–Keldysh effect or thermal heating of the sample under the electric field. PACS 71.20.Nr     

Characteristic features of optical absorption for Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> and NiO nanoparticles

The technical approach to determination of the structural and optical parameters of oxides with reduced dimensionality based on optical absorption measurements is described by example of gadolinium and nickel oxides. It was established that the temperature behavior of fundamental absorption edge for oxide nanoparticles is similar with the bulk materials with crystal structure. At the same time, the energy characteristics (band gap and effective phonon energies) for low-dimensional oxides are found to be significantly different from their bulk counterparts. The presented methodological method to obtain of qualitative and quantitative correlations of structural and optical characteristics provides novel reliable knowledge of nanoscaled 3d and 4f–metal oxide materials that is useful for development of their practical applications.     

Optical studies on the red luminescence of InGaN epilayers

Photoluminescence, photoluminescence excitation and time-resolved photoluminescence studies were performed in a partially relaxed InGaN epilayer, and exhibiting a 3D growth mode at the surface. Two emission bands, a red (centred at 1.88 eV) and a blue (centred at 2.58 eV) were observed. In order to investigate their origin and their relation with the strain relaxation along the growth direction, the sample was etched. After etching, only an asymmetrical broad emission band centred at 2.15 eV was observed.The decrease of decay time and the increase of the band edge absorption energy with increasing monitored photon energy, along the red emission, are assigned to the effect of localization of excitons at potential minima, originated in compositional and strain inhomogeneities of the sample. Therefore, the blue shift observed on this band with an increase in temperature, is caused by the population of higher energy states. The large difference between the luminescence intensities, decay times and the thermal quenching of the red and blue (centred at 2.58 eV) band is also accounted for by the localization model. It is demonstrated that the luminescence observed after etching is a superposition of two bands, one originated from the InGaN film, and the other from the GaN underlayer. The large difference between absorption and emission energies, compared with those measured in the as-grown sample, within the same spectral region, indicates that this emission has a different origin. It is suggested that deep levels might be responsible for the luminescence observed after etching.     

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.     

Optical properties and electronic structure of BiTeCl and BiTeBr compounds

Optical properties of BiTeCl and BiTeBr compounds with a strong Rashba spin–orbit coupling are studied in the 0.08–5.0 eV range using the optical ellipsometry method. Fundamental characteristics of the electronic structure are obtained. Similarly to BiTeI, spectra of the imaginary part of dielectric permittivity constant ε₂(E) in the energy interval between the plasma edge and the threshold of an intense interband absorption (0.7 eV in BiTeCl and 0.6 eV in BiTeBr) display a fine structure of electronic transitions at 0.25 and 0.55 eV in BiTeCl and 0.20 and 0.50 eV in BiTeBr. These features are assigned to electronic transitions between the bulk conduction zones split by the Rashba spin–orbit interaction. The parameters of the electronic structure of BiTeCl and BiTeBr are compared with the BiTeI compound that was studied earlier. In the BiTeCl–BiTeBr–BiTeI row, the absorption edge and main features of the fundamental absorption exhibit a shift to low energies.     

Application of the backscatter fundamental parameter method for in situ element determination using a portable energy‐dispersive x‐ray fluorescence spectrometer

The backscatter fundamental parameter (BFP) algorithm was adapted and modified for the use with a portable energy‐dispersive x‐ray fluorescence (EDXRF) spectrometer system. The method utilizes coherently and incoherently scattered peaks of primary radiation to estimate the ‘dark matrix’ of the analysed sample. A so‐called ‘full fundamental parameter’ model was implemented in the algorithm, allowing a simple calibration of the method using only one standard sample. To improve the accuracy of the method, the differential mass scattering cross‐sections were used. The algorithm also takes into account the secondary excitation effects. The method was applied to element determinations in various matrices with minimum sample preparation. It was tested in the laboratory with homogeneous samples prepared from standard reference materials and was also successfully applied to in situ element determinations in soil. The analyses were performed using a portable XRF spectrometer equipped with a ¹⁰⁹Cd radioisotope source and an Si‐PIN photodiode detector. The BFP algorithm was found to perform well for the analysis of loose powder samples containing an unknown fraction of ‘dark matrix,’ and therefore it is regarded as suitable for in situ element determinations. Copyright © 2003 John Wiley & Sons, Ltd.     

Time-resolved luminescence of LaBr3-Ce scintillation crystals upon selective UV-VUV-XUV excitation

The time-resolved photoluminescence (PL) of LaBr₃-Ce scintillation spectrometric crystals produced in Russia is measured upon excitation using synchrotron radiation with photon energies of 3.7–21 and 45–290 eV at temperatures of 295 and 7.5 K. The PL spectra and decay curves are measured for excitation in the transparency range, at the edge of fundamental absorption, at the interband transitions, and in the range of inner-shell absorption. It is demonstrated that the PL yield is not proportional to the excitation energy, and that the PL decay curves are modified in the range of photoionization of the 3d (Br) and 4d (La) inner shells and, especially, in the range of giant resonance.     

X射线荧光分析中X射线管原级能谱分布的测定

确切知道X射线管激发的原级能谱分布是X射线荧光分析中的一个重要前提,所用能谱分布函数的准确度大大影响了最终的测量结果。提出利用间接测量法,选用合适的参量模型来描述X射线的原级能谱分布。依靠实验测得的厚靶纯元素样品的荧光强度,利用已知的理论公式,建立非线性方程,优化得到参量模型中的参量值。通过比较实验测得的元素的荧光强度值和利用得到的能谱分布函数计算的理论值,证明此种方法是可行的。     

Non-linear photo-induced desorption of GaP

Laser-induced desorption of P from GaP at various photon energies near the absorption edge has been measured. The desorption yield is found to start increasing above a certain threshold laser fluence, of which the dependence on the photon energy exhibits a sharp dip near the indirect band gap besides a gradually decreasing component from the indirect band gap to the direct band gap energy. The sharp dip is ascribed to desorption induced by dense excitation of the surface states.     

Superradiance of a degenerate exciton gas in semiconductors with indirect fundamental absorption edge

It is predicted that superradiant states can be formed in a degenerate exciton gas in a semiconductor with an indirect fundamental absorption edge. The superradiance results from four-particle recombination processes and occurs at photon energies approximately twice as high as the band gap energy. Experimental results supporting the possibility of the observation of superradiance from SiGe/Si quantum wells are presented.     

一种完整测量磁光克尔效应和法拉第效应的方法

详细给出了一种测量完整克尔和法拉弟效应的原理和实验装置。该装置简单可靠,安全由计算机控制。利用傅里叶变换方法,实验系统可以在从０．０１度至几百度的克尔和法拉第旋转角范围内以及在１．５￣６．０ｅＶ的光子能量范围内,准确地测量克尔和法拉第旋转角范围内以及在１．５￣６．０ｅＶ的光子能量范围内,准确地测量克尔和法拉第效应的绝对值。作为实验测量的例子,给出了ＭｎＢｉＡｌ合金薄膜样品和ＧａＰ块状样品的克尔和法     

Electronic transitions,crystal field effects and phonons in UO2

An extensive optical study of the 5f magnetic semiconductor UO₂ is presented. The experimental data include near normal incidence reflectivity measurements from 0.0025 to 13 eV, absorption and Faraday rotation measurements as function of temperature and of magnetic fields up to 100 kOe and photoemission results.From the data in the fundamental absorption region an energy level scheme is derived. This level scheme differs markedly from an earlier model but it is quantitatively supported by a calculation using the thermochemical Haber-Born process and also by cluster calculations. The localized nature of the 5f electrons is demonstrated.The absorption edge at 2 eV shows an abrupt shift to lower energies at the first order phase transition of UO₂ to the antiferromagnetic state. This shift is shown to be larger than expected from the lattice contraction indicating a magnetic order induced contribution to the total red shift.Below the absorption edge, intra-5f transitions and multiphonon excitations are reported, showing striking order induced effects at and below T_N = 30.8 K.New results are presented for ε_st, ε_opt, ω_TO and ω_LO which fulfill the Lyddane-Sachs-Teller relation.