ISSN:0049-8246    

DOI:10.1002/xrs.1300230102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractFirst results from a new program for chemical characterization of environmental particulates using synchrotron radiation are described. Trace element concentrations and chemical state determinations were made on fly ash samples from lignite‐fired power stations. The experiments were based on the use of x‐rays produced by an electron beam passing a bending magnet at the Brookhaven National Synchrotron Light Source. The high brilliance, energy tunability and almost complete polarization of the x‐rays were used as the basis of a versatile X‐ray microscope (XRM) at the X26 beam line. Mössbauer spectroscopy was employed as a complementary method for determination of the compounds in the iron‐containing fly ash particles. The results demonstrate the practicality and strengths of using the synchrotron XRM for measurements of trace elements in fly ash particles and for the determination of oxidation states using x‐ray absorption near‐

ISSN:0049-8246    

DOI:10.1002/xrs.1300230103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA monochromatic high‐intensity x‐ray beam, obtained by Bragg reflection of the strongest characteristic tube line under small angles on single crystals, can be used as an EDXRF excitation source. A systematic selection procedure and search of 55 single crystals suitable as EDXRF Bragg reflectors was made and highly oriented pyrolytic graphite (HOPG) was found to be a superior candidate for the characteristic Kα line of an Mo tube within the range of low‐order reflections, yielding the highest intensities. Meridionally and sagitally curved HOPGs were studied in a flexible experimental set‐up and the reflected beam intensity and profile were compared with the corresponding data obtained from flat HOPGs with different mosaic spreads. The relationships between collimation, crystal curvature and mosaic spread were evaluated. The experimental angular beam acceptance and the secondary extinction effects dependent on the mosaic spread of the HOPG were found to be in line with theoretical expectations. Measured in similar configurations as required for realistic EDXRF applications, the sagitally bent HOPG increases the reflected beam intensity up to 77% whereas the meridionally bent HOPG yields an intensity gain of only up to 28% compared with the flat crystal with the same mosaic spread. The detection limits for the corresponding thin‐filter EDXRF analysis are

ISSN:0049-8246    

DOI:10.1002/xrs.1300230104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe presence of an unfilled inner electron shell in the rare earth elements is manifested in x‐ray absorption effects that are unique to the energy region including the Mα and Mβ lines of these elements. In contrast to the normal edge‐type absorption, this anomalous absorption appears as an absorption line. A method is presented here for the quantitative determination of the extent of this anomalous absorption. Solid bulk metal samples, excited with a monoenergetic electron beam, were examined with a wavelength‐dispersive x‐ray spectrometer. The discussed method makes the experimentally determined absorption independent of both the detection efficiency and atomic data such as the fluorescence yield and transition probabilities. A simple empirical model is proposed to explain the dependence of the absorption of the Mα line on the absorption path length, which was varied by the primary beam energy. Normal and anomalous absorption are treated as independent and competing processes in this model. Atomic data such as the mass absorption coefficients pertinent to the anomalous absorption of the Mα lines were also determined and ar

ISSN:0049-8246    

DOI:10.1002/xrs.1300230105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractCompton scattered radiation has been used as an internal standard to compensate for matrix absorption effects; it has also been used separately for background correction. In this work, the simultaneous matrix and background correction method was developed, in which both matrix absorption effects and background correction are performed simultaneously, thereby reducing the measurement time; this is particularly important when dealing with large numbers of samples. It also obviates the problem in the conventional method of correcting for the background when the interference‐free background position near the spectral peaks cannot be found. Application of this method to a large number of geological standard reference materials yields values of trace element concentrations in good agreement with their recommended value

ISSN:0049-8246    

DOI:10.1002/xrs.1300230106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA transmission‐type attachment for energy‐dispersive x‐ray fluorescence analysis was developed. The attachment was designed for analysis to be carried out in a CAMEBAX microanalyzer, where the energy‐dispersive spectrometer detector views the specimen through a hole in the objective lens and the space between the specimen and the pole piece of the objective lens is fairly small. Nevertheless, this type of attachment can be applied in other microanalyzers or scanning electron microscopes. Detection limits between 0.5 and 5 ppm on SRM 612 glass (NIST) and the applicability to the analysis of small particles (SRM 470 glass sphere 90 μm in diameter) are demo

ISSN:0049-8246    

DOI:10.1002/xrs.1300230107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe overlapping of characteristic spectral lines of two or more elemental constituents of a sample has always been a drawback in x‐ray fluorescence analysis. A new approach to solve this problem is presented, based in the excitation at two different energies. The results show that it is possible to calculate the concentration of elements with overlapped lines with high accuracy. We thus avoid the use of other means to obtain the needed number of spectral lines, such as secondary characteristic lines, which usually have a low peak to background ratio, or to recur to the line fraction (i.e. Kβ/Kα), which is matrix depend

ISSN:0049-8246    

DOI:10.1002/xrs.1300230108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe relationship between the fluorescent intensity ratio of analyte to pure analyte/concentration of analyte and the fluorescent energy can be expressed as In(Ii/Ii0ci) =aInEi+b, whereaandbare constants for a given matrix. This relationship depends on the pure element intensityIi0. Experimental pure element intensities can be obtained in a number of ways. Although the use of thick pure metal foils is perhaps the simplest, there are many elements for which pure metal foils are not available. This paper discusses the determination of experimental values of pure element intensities from their oxides and shows that their values are in good agreement with those obtained from pure metal foils.

ISSN:0049-8246    

DOI:10.1002/xrs.1300230109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0049-8246    

DOI:10.1002/xrs.1300230110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0049-8246    

DOI:10.1002/xrs.1300230111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY