An increase of utilization efficiency of X-ray beam

The features of absorbed dose field formation in objects irradiated with scanned X-ray beams at double—and four-sided irradiation were investigated both analytically and by Monte Carlo methods. An analytical approach uses an angular/spectrum X-ray characteristics calculated with PENELOPE, JEANT 4 and ModeXR codes. It was shown that the special angular orientation of electron beam incidence on the X-ray converter leads to X-ray dose smoothing on the surface of the irradiated object. At the same time, a double-sided irradiation can provide high X-ray beam efficiency at dose uniformity ration (DUR) <1.5 for sizeable object thickness. At four-sided irradiation, the angular orientation of electron beam incidence on the X-ray converter should be changed so as to focus the electrons to the center of the converter. At this mode X-ray beam efficiency is more than 60%.     

Influence of X-ray tube spectral distribution on uncertainty of calculated fluorescent radiation intensity

The relative radiation intensity (R_i) defined as fluorescent radiation intensity of analyte in specimen to fluorescent radiation intensity of pure element or compound, e.g., oxide is used in calculation in both fundamental parameter methods and in theoretical influence coefficient algorithms. Accuracy of calculated R_i is determined by uncertainties of atomic parameters, spectrometer geometry and also by X-ray tube spectral distribution. This paper presents the differences between R_i calculated using experimental and theoretical X-ray tube spectra evaluated by three different algorithms proposed by Pella et al., Ebel, and Finkelshtein–Pavlova. The calculations are performed for the most common targets, i.e., Cr, Mo, Rh and W. In this study, R_i is calculated for V, Cr, Mn, Fe, Co, Ni, Cu and Mo in steels as an example. The differences between R_i calculated using different X-ray tube spectrum algorithms are presented when pure element standard, multielement standard similar to the analyzed material and one pure element standard for all analytes is used in X-ray fluorescence analysis. The differences between R_i for intermediate-thickness samples (and also for thin films) and for X-ray tube, which ran for many hours, are also evaluated.     

Upper and lower bounds to partition functions for molecules with double minimum potentials

Upper and lower bounds to the vibrational partition function q for molecules with double minimum potentials are derived. Both the exact lower (Gibbs-Bogoliubov) and upper (Golden-Thompson) bound to q are evaluated analytically for the harmonic oscillator perturbed symmetrically or asymmetrically by a gaussian barrier. For the quadratic-quartic oscillator only the lower bound can be evaluated analytically, whereas the upper bound leads to a strongly divergent series resisting conventional surnmability techniques. In this case the classical partition function is used as an upper bound.     

Improved signal-to-noise ratio in laboratory-based phase contrast tomography

In conventional X-ray microtomography (μCT), the three-dimensional (3D) distribution of the attenuation coefficient of X-rays is measured and reconstructed in a 3D volume. As spatial resolution increases, the refraction of X-rays becomes a significant phenomenon in the imaging process. Although this so-called phase contrast was initially a cumbersome feature in lab-based μCT, special phase retrieval algorithms were developed to exploit these effects. Clear advantages in terms of visualization and analysis can be seen when phase retrieval algorithms are applied, including an increased signal-to-noise ratio. In this work, this is demonstrated both on simulated and measured data.     

The electrical neutrality of atoms

An atomic beam deflection experiment is described which establishes upper limits to the electrical charges of potassium and cesium atoms ofq(K)<2.4×10^?18 q _e andq(Cs)<3.0×10^?18 q _e at the 90% confidence level, in whichq _e is the electron charge magnitude. If we assume that the electron neutrino charge is zero and that charge conservation holds in neutron beta decay, then the difference δq in the electron and proton charge magnitudes has the upper limit δq<1.3×10^?20 q _e at the 90% confidence level. The possibility of a more sensitive atomic beam deflection experiment using a laser-cooled atomic beam is suggested. A brief review of the topic of the electrical neutrality of atoms is given.     

A Novel in Situ Oxidization-Sulfidation Growth Route via self-Purification Process to β-In2S3 Dendrites

A novel in situ oxidization-sulfidation growth route via a self-purification process has been developed to synthesize β-In₂S₃ dendrites. To our best knowledge, this is the first example to prepare dendrites of III-VI compounds, which are expected to show particular physical properties. The X-ray analysis (EDXA), X-ray photoelectron spectra (XPS), Raman spectrum and optical properties of β-In₂S₃ dendrites have also been investigated. It is found that the product is pure In₂S₃ and shows the strong quantum confinement of the excitonic transition expected for the In₂S₃ dendrites.     

The new X-ray mapping: X-ray spectrum imaging above 100 kHz output count rate with the silicon drift detector.

Electron-excited X-ray mapping is a key operational mode of the scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometry (EDS). The popularity of X-ray mapping persists despite the significant time penalty due to the relatively low output count rates, typically less than 25 kHz, that can be processed with the conventional EDS. The silicon drift detector (SDD) uses the same measurement physics, but modifications to the detector structure permit operation at a factor of 5-10 times higher than conventional EDS for the same resolution. Output count rates as high as 500 kHz can be achieved with 217 eV energy resolution (at MnKalpha). Such extraordinarily high count rates make possible X-ray mapping through the method of X-ray spectrum imaging, in which a complete spectrum is captured at each pixel of the scan. Useful compositional data can be captured in less than 200 s with a pixel density of 160 x 120. Applications to alloy and rock microstructures, ultrapure materials with rare inclusions, and aggregate particles with complex chemistry illustrate new approaches to characterization made practical by high-speed X-ray mapping with the SDD.Note: The Siegbahn notation for characteristic X-rays is commonly used in the field of electron beam X-ray spectrometry and will be used in this article. The equivalent IUPAC notation is indicated in parentheses at the first use.In this article, the following arbitrary definitions will be used when referring to concentration (C) ranges: major: C > 0.1 (10 wt%), minor: 0.01 相似文献   

Development of an X-ray detector using surface plasmon resonance

A new X-ray detector using surface plasmon resonance (SPR) is proposed. The detector consists of a prism coated with a thin metal film and semiconductor film. Optical laser pulse induces SPR condition on the metal surface, and synchronized X-ray pulse which is absorbed into the semiconductor film can be detected by measuring the change of the resonance condition of the surface plasmon. The expected time and spatial resolution of this detector is better than that of conventional X-ray detectors by combining this SPR measurement with ultra-short laser pulse as the probe beam. Our preliminary investigation using Au and ZnSe coated prism implies this scheme works well as the detector for the ultra-short X-ray pulse.     

Energy-resolved X-ray imaging

An investigation method of spatial distribution of separate chemical elements, contained in samples complex chemical composition, using an X-ray CCD-camera is considered. The camera records a fluorescence of the chemical elements of the sample, excited by a radiation of a static X-ray tube. An image is built at a CCD matrix with a pinhole camera. The CCD-camera operates in a regime of a multi-frame spectral recording of separate photons, in which it is possible to identify both the energy of the incident quanta, and the coordinate of the point of incidence in each frame. Analysis of the formed data array makes it possible to obtain the spatial distribution of the elements, contained in the sample discretely on Z (atomic number). Investigation results of the CCD-camera characteristics, algorithms of the computer software of the data processing, and examples of the obtained images are presented in the paper. It is shown that using this method it is possible to get distribution patterns of the chemical elements in the multi-component samples with the spatial distribution up to ≈ 15–20 μm.     

Spectral unmixing and clustering algorithms for assessment of single cells by Raman microscopic imaging

A detailed comparison of six multivariate algorithms is presented to analyze and generate Raman microscopic images that consist of a large number of individual spectra. This includes the segmentation algorithms for hierarchical cluster analysis, fuzzy C-means cluster analysis, and k-means cluster analysis and the spectral unmixing techniques for principal component analysis and vertex component analysis (VCA). All algorithms are reviewed and compared. Furthermore, comparisons are made to the new approach N-FINDR. In contrast to the related VCA approach, the used implementation of N-FINDR searches for the original input spectrum from the non-dimension reduced input matrix and sets it as the endmember signature. The algorithms were applied to hyperspectral data from a Raman image of a single cell. This data set was acquired by collecting individual spectra in a raster pattern using a 0.5-??m step size via a commercial Raman microspectrometer. The results were also compared with a fluorescence staining of the cell including its mitochondrial distribution. The ability of each algorithm to extract chemical and spatial information of subcellular components in the cell is discussed together with advantages and disadvantages.     

A method based on stochastic resonance for the detection of weak analytical signal

An effective method for detection of weak analytical signals with strong noise background is proposed based on the theory of stochastic resonance (SR). Compared with the conventional SR-based algorithms, the proposed algorithm is simplified by changing only one parameter to realize the weak signal detection. Simulation studies revealed that the method performs well in detection of analytical signals in very high level of noise background and is suitable for detecting signals with the different noise level by changing the parameter. Applications of the method to experimental weak signals of X-ray diffraction and Raman spectrum are also investigated. It is found that reliable results can be obtained.     

Three-dimensional Quantitative Structure-Activity Relationship Analyses of a Series of Butenolide ETA Antagonists

Two kinds of Three-dimensional Quantitative Structure-activity Relationship(3D-QSAR) methods,comparative molecular filed analysis(CoMFA) and comparative molecular similarity indices analysis (CoMSIA) ,were applied to analyze the structure-activity relationship of a series of 63 butenolide ETA selective antagonists with respect to their inhibition against human ETA receptor,The CoMFA and CoMSIA models were developed for the conceivable alignment of the molecules based on a template structure from the crystallized data.The statistical results from the initial orientation of the aligned molecules show that the 3D-QSAR model from CoMFA(q^2=0.543) is obviously superior to that from the conventional CoMSIA(q^2=0.407).In order to refine the model,all-space search (ASS) was applied to minimize the field sampling process.By rotating and translating the molecular aggregate within the grid systematically,all the possible samplings of the molecular fields were tested and subsequently the one with the highest q^2 was picked out .The comparison of the sensitivity of CoMFA and CoMSIA to different space orientation shows that the CoMFA q^2 values are more sensitive to the translations and rotations of the aligned molecules with respect to the lattice than those of CoMSIA.The best CoMFA model from ASS was further refined by the region focused technique.The high quality of the best model is indicated by the high corss-validated correlation and the prediction on the external test set.The CoMFA coefficient contour plots identify several key features that explain the wide range of activities,which may help us to design new effective ETA selective antagonists.     

Recalibration of a gas-sensor array system related to sensor replacement

Univariate multiplicative drift correction and multivariate component correction were applied for recalibration of long-term measurement data acquired with a solid-state gas-sensor array system. The efficiency of the methods was evaluated by classifying recalibrated measurement data using k-nearest neighbor classification and partial least-squares discriminant analysis. For the measurement data in this experiment both multiplicative drift correction and component correction appeared to be useful for recalibration of measurement data from the new gas-sensor array with regard to measurement data acquired with the old replaced gas-sensor array.     

Anomalous small-angle x-ray scattering from mesoporous noble metal catalysts

We present the analysis of a catalyst containing platinum nanoparticles supported on mesoporous MCM-41 silica by anomalous small-angle x-ray scattering (ASAXS). The analysis of this composite system by ASAXS is first studied by use of model calculation. Here, it is shown that the full analysis must proceed by decomposing the scattering data measured at different energies of the incident beam into three partial intensities. This evaluation is compared to a simplified method in which scattering curves measured at two different energies are subtracted from each other. The different methods are applied to experimental data obtained from platinum nanoparticles on an MCM-41 support material. The model calculations show that the simplified method leads to large deviations especially at low q in ordered systems. In the semi-ordered material MCM-41, these deviations are less pronounced, and the method of simple subtraction proves to be a good approximation for q values higher than 0.1 nm^?1.     

Stacked partial least squares regression analysis for spectral calibration and prediction

Two novel algorithms which employ the idea of stacked generalization or stacked regression, stacked partial least squares (SPLS) and stacked moving‐window partial least squares (SMWPLS) are reported in the present paper. The new algorithms establish parallel, conventional PLS models based on all intervals of a set of spectra to take advantage of the information from the whole spectrum by incorporating parallel models in a way to emphasize intervals highly related to the target property. It is theoretically and experimentally illustrated that the predictive ability of these two stacked methods combining all subsets or intervals of the whole spectrum is never poorer than that of a PLS model based only on the best interval. These two stacking algorithms generate more parsimonious regression models with better predictive power than conventional PLS, and perform best when the spectral information is neither isolated to a single, small region, nor spread uniformly over the response. A simulation data set is employed in this work not only to demonstrate this improvement, but also to demonstrate that stacked regressions have the potential capability of predicting property information from an outlier spectrum in the prediction set. Moisture, oil, protein and starch in Cargill corn samples have been successfully predicted by these new algorithms, as well as hydroxyl number for different instruments of terpolymer samples including and excluding an outlier spectrum. Copyright © 2009 John Wiley & Sons, Ltd.     

Benefits of X-Ray Spectrum Simulation at low Energies

 There are particular benefits in spectrum simulation for the interpretation of characteristic X-ray peaks below about 2 keV in energy, where peak overlaps, a sloping background and changing detector efficiency make it difficult to measure true peak intensities. Despite these difficulties, we have shown that a useful accuracy of simulation is possible without major revision of the existing theory, allowing the electron microprobe user to compare on-line a measured spectrum with one synthesised from an assumed sample composition. As part of a wider study, we have used a database of X-ray spectra from 150 samples of known composition to confirm the accuracy of simulation over the energy range from 0.28–1.9 keV, finding an RMS error of better than 8%. The database included 181 Kα, Lα and Mα peaks from elements of atomic number 6–77, excited by beam voltages from 5–30 kV. Central to the method is the use of the ratio of (Peak Intensity)/(Total Background Intensity), which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions. Examples are given to illustrate the use of the simulator in helping to choose the best conditions for analysis, and as an aid in interpreting the spectra so obtained. Both modes of operation are iterative in nature and require a fast and accurate simulator that is easy to use. Further development will be guided by experience in its use.     

Photocapacitance spectroscopy of thin film cadmium selenide electrodes

Photocapacitance spectroscopic measurements were made on thin film CdSe that was prepared by electrodeposition from a solution of selenosulfite and cadmium ions. The spectra were very similar for five spots on three films that were prepared under identical conditions. In 0.5 M KOH solution, the film appeared stable for a number of measuremens at various applied potentials. At pH 10 the film was relatively stable for applied potentials negative of 0.0 V (SCE). At more positive potentials in this solution, surface oxidation appears to occur, resulting in the formation of a surface layer that alters the spectrum. In both solutions, the photocapacitance spectrum appears independent of applied potential over the range employed. The continuous rise without any abrupt steps in the spectrum as the photon energy is increased indicated that there are probably a series of bandgap states of comparable density. The energy levels range from E_c − 1.1 eV to E_c − 1.6 eV. In contrast with thin film CdSe prepared by vacuum coevaporation, the electrodeposited material did not require low frequency (7 to 70 Hz) for the measurement.     

Reduction of beta-interference in gamma-spectrometric measurements of neutron-irradiated geological material

The analytical technique for instrumental neutron activation analysis, when applied to geological materials, is improved by introducing an lectromagnetic field between sample and detector. This field lowers the bremsstrahlung background intensity in the gamma-spectrum, by reducing the number of beta-particles reaching the detector. Thus, precision, accuracy and lower detection limit are improved. In this work the technique has been used on an alkalisyenite and on meteoritic material, rocks containing high quantities of sodium and iron, respectively. After neutron irradiation, the induced nuclides²⁴Na and⁵⁹Fe are responsible for high bremsstrahlung interference, which under normal analytical conditions would mask any X-ray or gamma-ray peaks of interest. The technique is easily applied to multielement analysis of geological and biological material (although the latter is not treated in this paper). It can be combined with sophisticated spectrum-treating techniques such as spectrum stripping and spectrum smoothing, or coincidence-anticoincidence circuits.     

Study on the influence of X-ray tube spectral distribution on the analysis of bulk samples and thin films: Fundamental parameters method and theoretical coefficient algorithms

Knowledge of X-ray tube spectral distribution is necessary in theoretical methods of matrix correction, i.e. in both fundamental parameter (FP) methods and theoretical influence coefficient algorithms. Thus, the influence of X-ray tube distribution on the accuracy of the analysis of thin films and bulk samples is presented. The calculations are performed using experimental X-ray tube spectra taken from the literature and theoretical X-ray tube spectra evaluated by three different algorithms proposed by Pella et al. (X-Ray Spectrom. 14 (1985) 125–135), Ebel (X-Ray Spectrom. 28 (1999) 255–266), and Finkelshtein and Pavlova (X-Ray Spectrom. 28 (1999) 27–32). In this study, Fe–Cr–Ni system is selected as an example and the calculations are performed for X-ray tubes commonly applied in X-ray fluorescence analysis (XRF), i.e., Cr, Mo, Rh and W. The influence of X-ray tube spectra on FP analysis is evaluated when quantification is performed using various types of calibration samples. FP analysis of bulk samples is performed using pure-element bulk standards and multielement bulk standards similar to the analyzed material, whereas for FP analysis of thin films, the bulk and thin pure-element standards are used. For the evaluation of the influence of X-ray tube spectra on XRF analysis performed by theoretical influence coefficient methods, two algorithms for bulk samples are selected, i.e. Claisse–Quintin (Can. Spectrosc. 12 (1967) 129–134) and COLA algorithms (G.R. Lachance, Paper Presented at the International Conference on Industrial Inorganic Elemental Analysis, Metz, France, June 3, 1981) and two algorithms (constant and linear coefficients) for thin films recently proposed by Sitko (X-Ray Spectrom. 37 (2008) 265–272).