ISSN:0049-8246    

DOI:10.1002/xrs.1300070402

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

年代:1978

数据来源: WILEY

摘要:

AbstractExperimental and theoretical studies of fine electron beam interactions with film specimens are described. It is shown that a Monte Carlo‐based method for plotting electron trajectories can give good indications of both X‐ray spatial resoultion and sensitivity as experienced during X‐ray microanalysis in scanning transmission electron microscopes (STEM). The main operational parameters considered are aperture and lens settings, beam accelerating voltage and specimen thickness. Based on theroretically and experimentally determined data, as set of conditions for optimum X‐ray detection sensitivity and X‐ray spatial resoultion for nickel and aluminium are presented. It is shown that little advantage is gained by performing X‐ray microanalysis at beam accelerating voltages greater than 100kV. Also the necessity to condense the beam spot size to less than 100 Å is relatively unimportant from the viewpoint of improving X‐ray spatial reso

ISSN:0049-8246    

DOI:10.1002/xrs.1300070403

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

年代:1978

数据来源: WILEY

摘要:

AbstractIt is demonstrated that an evalution procedure for conversion X‐ray intensity to element concentration used on an existing spectrometer can be used in reverse to provide intensity data for calibrating another spectrometer. Extensive remeasurement o standards is therby eliminated. Intensities are calulated for postulated changes in compostion and these form the input data for the spectrometer computer regression program. Such data are free from measurement error. Calibration and α coefficents from claulated intensities are found to give analytical results of an accuracy comparable with those derived from experimentally produced calibration. The intensity calculations can be extended to include the determination of calibration and α coefficents without using the sepctrometyer regression programs. Considedrable expense and effort can be sa

ISSN:0049-8246    

DOI:10.1002/xrs.1300070404

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

年代:1978

数据来源: WILEY

摘要:

AbstractAn equation has been derived for the computaion of the standard deviation of the results of X‐ray micro analysis. The contributions of partial standard deviations of all magnitudes are included. The equation is gernerally applicable to multiple measurements and various methods of measurement

ISSN:0049-8246    

DOI:10.1002/xrs.1300070405

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

年代:1978

数据来源: WILEY

摘要:

AbstractAn empirical model that includes the effect of incidence and exit angles and non‐random packing effects is proposed for describing the effect of particle size on the measured X‐ray fluorescence (XRF) response from thick heterogeneous samples. An exact model is derived that illustrates these effects for the ideal case of reglarly oriented cubes, and the previous models at high concentrations of a single homogeneous particale the proposed model and the previous models at high concentrations of a single homogeneous particle type where the largest difference between the previous models is observed. It is shown that at specific angles of incidence and exit the proposed model agrees closely with each of the earlier models. Experimental data taken at different incidence angles show that the proposed model provides the best least‐squares fit to the observed data on the basis of the minimum reduced chi‐squar

ISSN:0049-8246    

DOI:10.1002/xrs.1300070406

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

年代:1978

数据来源: WILEY

摘要:

AbstractMathermatical techniques (Fourier transform and iterative procedures) are described for unfolding spectrometer broadening from observed X‐ray emission peaks. This enables enhanced resolution to be obtained. Broadening introduced by soller collimators and by crystal imperfections are considered in detail. Low energy peak ‘tailing’ due to beam divergence in the plane of the soller slits is also disc

ISSN:0049-8246    

DOI:10.1002/xrs.1300070407

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

年代:1978

数据来源: WILEY

摘要:

AbstractThree X‐ray spectrometric procedures have been developed to directly measure the Ga content in binary PuGa alloys. In one procedure en energy‐dispersive spectrometer is used; in the other two a wavelengh‐dispersive spectrometer is used. Certified reference alloys with known Ga content have been produced, and simple procedures to handle them safely have been developed. We have constructed an energy‐dispersive spectrometer system for analyzing Pu‐containing materials and charactrerized the low energy gamma‐ray s

ISSN:0049-8246    

DOI:10.1002/xrs.1300070408

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

年代:1978

数据来源: WILEY

摘要:

AbstractFor application for the fundamental parameter approach to quantitative chemical analysis of mixtures by X‐ray fluorescence, accrate knowledge is required of fluroescence yields and ralative intensities of X‐ray lines of the various elements involved. The spread in published data suggests, however, that these parameters are not known with as much accuracy as could be used profitably. In this paper we describe a method by which K‐shell flurescence yield and Kα/Kβ intensity ratio can both be measured in the same experiment to within approximately 0.5% for pure elements available as thin polcrystalline foil. Results are given for the particular case of nickel (Z=28) for which we find ωK= 0.452 ± 0.002 and Kα/Kβ=6.91 ± 0.335, but the method is readily applicable to anty element whose atomic number falls in the approximate range 20 ≲Z≲ 50 and which can be obtained in suitable physical form. A key factor in the experimental design is use of a non‐dispersive (intrinsic germanium) X‐ray analyzer; this makes it possible to employ a very simple transmission geometry which can be characterized quite precisely. Experimental conditions, and precautions needed to obtain accurate and consistant results, are described in some detail. Among other corrections applied, allowance is made for scattering of both exciting statistics and residual uncertaintes incalculating corrections for scattering. Among these residual uncertainties are errors in correcting scattering coefficients for anomalous dispersion. Such errors are significant only when evaluatingfK, the K‐shell excitation efficienvcy; the important productfKωKcan, however, be determined (fKωK= 0.398 ± 0.002) with greater

ISSN:0049-8246    

DOI:10.1002/xrs.1300070409

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

年代:1978

数据来源: WILEY

摘要:

AbstractCoherent and incoherent scattering processes are commonly ignored, or at best estimated only crudely, in X‐ray fluorescence experimently designed either to measure physical constants or to effect nondestructive chemical analysis of mixtures and alloys. The influence of this scattering is of second order, but is nevertheless large enough (generally 2–5%) to overshadow inherent errors in experimental measurement. In this paper, we develop a formalsim for calculating scattering corrections applicable to experiments involving either thin polycrystalline or amorphus samples studied in transmission or thick samples of a similar kind examined using reflection geometry. Our principal approximations are physical; we assume (i) that crystal line structure and texture in the sample serve merely to modulate the angular distribution of coherent scattering can be ignored. Mathermatical development of the model is essentially exact. Adequacy of approxination (i) is supported by previously published experimental and theoretical work; as for approximation (ii), we have found that results do not depend crucially upon the particular angular distribution function assumed for scattering. We believe, at a conservative estimate, that overll errors in our scattering corrections are in almost all cases of interest less than 25%; data to which they are applied, therefore are, potentially accrate to better than 0.5–1.25% Three important effects have to be considered: (a) the generation of fluorescence radiation which has been scattered within the sample,(b)the scattering of fluorescent radiation away from the acceptance aperture of lthe detector, and (c)the scattering of fluorescent radiation into this aperture. In our formalism, only (a)and (c)need be calculated explicityly. Corrections are expressed simply as products of quotients σ/μ with certain enhancement terms (μ being a total attenuation constant and σ an attenuation constant for scattering). In transmission geometry, the enhancement terms are complicated functions of transmission factors for exciting and fluorescent radiations only and, in reflection geometry, they are simpler functions of angles specified by the experimental arrangement used and the total attenuation constants for exciting and fluorescent radiations. It turns out in many cases that (c) above is the predominant effect and, commonly, the positive contribution to measured fluorescent intensity made by scatting into the detector outweighs substantially the negative contribution made by scattering out of the detector. Results are also expressed in simple graphical form in terms of effective attenuation constants for exciting and fluorescent radiations; in this form they are readily available for use by the reader without the necessity for further calculation. Surprisingly, effective attenuation constants are generally smaller, often consideraby smaller, than constants representing photoelectric absorpt

ISSN:0049-8246    

DOI:10.1002/xrs.1300070410

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe Properties of diffracting crystals a Bragg and of near 45° are studied for use as an X‐ray polarizer. Such crystals have many advantages over the Barkla type polarizer when used in an energy‐dispersive X‐ray analyzer. The study shows that many matching λ‐d combinations are available, but the present work was done with LiF (200). With this crystal, the second order diffraction of Cu Kβ radiation occurs at 43.67° and an improvement of peak to background ratio by a factor 45 was obtained. The study revealed that a substantial improvement of peak to minimum detection limit can be obtained with a larger deviation of the polarization angle, as long as this deviation is accompanied by a higher X

ISSN:0049-8246    

DOI:10.1002/xrs.1300070411

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

年代:1978

数据来源: WILEY