ISSN:0049-8246    

DOI:10.1002/xrs.1300120402

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe application limits of a correction method for the particle‐size effect in x‐ray fluorescence (XRF) analysis are estimated theoretically in the presented paper. This correction method requires the use of two sources of exciting γ‐or x‐radiation of different energies.1The influence of the different values of the parameter t′ (which is a function of the linear absorption coefficients for primary and fluorescent radiation) and the influence of the relative standard deviation,Sr(resulting from counting statistics) have been taken into account in evaluating the efficiency of the method. In addition, the criteria for the selection of the optimum energies of the exciting radiation, the proper times of measurement and the activities of the sources of primary radiation are proposed. An example of the application of the proposed criteria to the determination of iron (as Fe3O4) is

ISSN:0049-8246    

DOI:10.1002/xrs.1300120403

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

年代:1983

数据来源: WILEY

摘要:

AbstractPIXE (particle induced x‐ray emission) analysis of aerosols has been applied to four different samplers to determine sample thickness corrections, detection limits and required sampling times in different environments. The samplers (two total filter samplers, a two stage filter sampler and a cascade impactor) were used with filters made by Ghia, Millipore, Nucleopore and backings of polystyrene film, respectively. The calculations were based on the accumulation mode aerosol (particles in the 0.05–2μm diameter range) composition. Sampling times (resulting in detection limits 10 times lower than assumed aerosol concentrations) ranged from a quarter of an hour in urban, to a quarter of a day in rural and to two weeks in remote environments. These sampling times are calculated with the requirement that at least one element representing each of the following sources was detected: fossil fuel combustion (S, V and Ni), leaded petrol combustion (Br and Pb) and general industrial activities (Cr, Cu and Zn). Generally the two stage filter sampler employed with Nuclepore filters yielded the highest time resolution when specific flow rate, thickness and substrate impurities were taken into consideration. Thickness corrections based on a proton energy of 2.55 MeV and typical ambient urban and rural aerosol matrices show that elements of low atomic number such as P, S and Cl, where the x‐ray self absorption effect is most important, require a 10–20% correction with a uniform deposit thickness of about 0.5 mg cm−2and a non‐nuniform (conical) deposit thickness of about 1 mg cm−2. For elements of higher atomic number than vanadium (K x‐rays) the proton energy loss correction dominates. Sampling times resulting in the above mentioned deposit thicknesses were shortest for the cascade impactor while the Millipore and Nuclepore filter samplers were least critical

ISSN:0049-8246    

DOI:10.1002/xrs.1300120404

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

年代:1983

数据来源: WILEY

摘要:

AbstractA method has been investigated which allows calculations of the absorption correction factors in the energy range 1.0–5.0 keV using55Fe excitation source. From the experimentally‐measured absorption factors between 6.0 and 20.0 keV using109Cd excitation source, the coefficients at lower energies with the associated absorption jumps are generated through an iterative proced

ISSN:0049-8246    

DOI:10.1002/xrs.1300120405

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

年代:1983

数据来源: WILEY

摘要:

AbstractA new radioisotope excited x‐ray fluorescence (XRF) technique which employs source‐samples has been applied for the determination of low Z elements in geological materials. The source‐samples is prepared by directly inserting about 100 μCi of the radioisotope (Fe‐55) into about 10–20 mg of the sample in its holder and placing this directly on the face of the detector window. The precision (relative total standard deviation) of this technique for K2O%, CaO% and TiO2% is about 4% and is compared to conventional radioisotope excited XRF. Finally, the accuracy of this technique is shown by the analysis of five geological reference materials as well as compared to conventional radioisotope e

ISSN:0049-8246    

DOI:10.1002/xrs.1300120406

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

年代:1983

数据来源: WILEY

摘要:

AbstractCross‐sections for bremsstrahlung production in thin films may be derived theoretically only if certain approximations are made or if there is recourse to numerical techniques. In this paper, two approximate equations, one based on the Sommerfeld theory and the other on the Bethe–Heitler theory, are assessed for their accuracy in predicting cross‐sections differential in photon energy and emergence angle when a thin foil target is bombarded with electrons with energies between 40 and 100 keV. Experimental data are presented from eight different target materials and these are processed initially to make comparisons between experimental and theoretical spectral shapes and subsequently to compare observed and predicted absolute cross‐section values. Except for the heaviest target material (Au), the Bethe–Heitler theory provided a satisfactory description of all experimental observations. In contrast, the Sommerfeld theory provided a significantly inferior description of spectral shapes and consistently overestimated absolute cross‐section

ISSN:0049-8246    

DOI:10.1002/xrs.1300120407

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

年代:1983

数据来源: WILEY

摘要:

AbstractTwo approximate theories are considered for the production of characteristic x‐rays when thin foil targets are bombarded with electrons with energies between 40 and 100 keV. One, due to Kolbenstvedt, is semi‐classical in nature whilst the other, due to Bethe, contains two parameters which are normally adjusted empirically. Data from six different target materials are presented, but because errors in experimentally derived absolute cross‐sections are large, a comparison is made between theoretical and observed ratios of characteristicKα photons to bremsstrahlung photons in a 20 eV channel directly beneath the peak. By adjusting the Bethe parameters and using a modified Bethe‐Heitler theory to predict the bremsstrahlung, agreement between experiment and theory of typically 10% is recorded. Finally, a means of simplifying the equations used to enable rapid calculation of x‐ray spectra with a pocket calculator is

ISSN:0049-8246    

DOI:10.1002/xrs.1300120408

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

年代:1983

数据来源: WILEY

摘要:

AbstractA method for measuring the surface density of pure element thin films using x‐ray fluorescence and coherent scattering of primary radiation has been developed. The accuracy is greatly improved by intensity ratio measurements where the dependence on the accuracy of the fundamental parameters is eliminate

ISSN:0049-8246    

DOI:10.1002/xrs.1300120409

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

年代:1983

数据来源: WILEY

摘要:

AbstractK x‐ray production cross‐sections of Ag, Sn and Te by 32‐80 MeV32S ions have been measured. The dependence of target K x‐ray yields on the target thickness was found to be negligible in the S (64 MeV) + Ag collision system. The experimental data are compared with some theoretical pred

ISSN:0049-8246    

DOI:10.1002/xrs.1300120410

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe construction of a mobile XRF unit is described. It consists of a radionuclide source (109Cd), shielding, a sample exchanger for powdered samples, a semiconductor detector and an electronic measuring and evaluation system. The disadvantage of the supply of liquid nitrogen or liquid air for the semiconductor detector is avoided by use of a mobile unit for the production of liquid air constructed for this purpose. Numerous measurements were carried out at several location within the Federal Republic of Germany.

ISSN:0049-8246    

DOI:10.1002/xrs.1300120411

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

年代:1983

数据来源: WILEY