Measurement and Calculation of X-Ray Production Efficiencies for Copper, Zirconium, and Tungsten.

Electron probe microanalysis (EPMA) is based on physical relations between measured X-ray intensities of characteristic lines and their X-ray production efficiency, which depends on the specimen composition. The quality of the analysis results relies on how realistically the physical relations describe the generation and emission of X-rays. Special experiments are necessary to measure X-ray production efficiencies. A challenge in these experiments is the determination of the detection efficiency of the spectrometer as a function of the photon energy. An energy-dispersive spectrometer was used in this work, for which the efficiency was determined at metrological synchrotron beamlines with an accuracy of ±2%. X-ray production efficiencies for the L series and the Kα series of copper and zirconium and for the M and L series of tungsten were determined at energies up to 30 keV in a scanning electron microscope. These experimental values were compared with calculated X-ray production efficiencies using physical relations and material constants applied in EPMA. The objective of the comparison is the further improvement of EPMA algorithms as well as extending the available database for X-ray production efficiencies. Experimental data for the X-ray production efficiency are also useful for the assessment of spectrum simulation software.

Determination of the Effective Detector Area of an Energy-Dispersive X-Ray Spectrometer at the Scanning Electron Microscope Using Experimental and Theoretical X-Ray Emission Yields.

A method is proposed to determine the effective detector area for energy-dispersive X-ray spectrometers (EDS). Nowadays, detectors are available for a wide range of nominal areas ranging from 10 up to 150 mm2. However, it remains in most cases unknown whether this nominal area coincides with the "net active sensor area" that should be given according to the related standard ISO 15632, or with any other area of the detector device. Moreover, the specific geometry of EDS installation may further reduce a given detector area. The proposed method can be applied to most scanning electron microscope/EDS configurations. The basic idea consists in a comparison of the measured count rate with the count rate resulting from known X-ray yields of copper, titanium, or silicon. The method was successfully tested on three detectors with known effective area and applied further to seven spectrometers from different manufacturers. In most cases the method gave an effective area smaller than the area given in the detector description.

Reinvestigation of the M emission spectrum of uranium-92.

The M spectrum of the element uranium was reinvestigated by using both high-resolution wavelength dispersive (WD) spectrometry as well as energy dispersive (ED) spectrometry. Thereby we observed relative intensities that deviate from data in the literature. These discrepancies were not only observed for the weak U M lines but also for major lines. By measuring the Mα,ß region of the spectrum with a PET crystal in second-order reflection, a sufficient energy resolution was achieved to separate Mα(2) (M(5)N(6)) from Mα(1) (M(5)N(7)). The intensity ratio I(M(5)N(6))/I(M(5)N(7)) was determined to be approximately 5%, which is in strong contrast to the data tabulated by White and Johnson [White, E.W. & Johnson, G.G. (1970). X-Ray and Absorption Wavelengths and Two-Theta Tables. ASTM Data Series DS37A, 2nd ed. Philadelphia, PA: American Society for Testing and Materials]. Furthermore M(5)N(7) was clearly observed as the strongest of the M lines that disagrees with data presented by Kleykamp [Kleykamp, H. (1981). Wavelengths of the M X-ray spectra of uranium, neptunium, plutonium, and americium. Z Naturforsch 36a, 1388-1390], who reported Mß (M(4)N(6)) as the strongest line. Also, after White and Johnson (1970), the line M(2)N(4) should be more intense than M(3)O(5) by a factor of 5. Both our WD and ED spectra show clearly that M(3)O(5) is stronger than M(2)N(4). Altogether, we observed in our WD spectra 26 M lines. In some cases untypical large differences between the line energies given by Bearden [Bearden, J.A. (1967). X-ray wavelengths. Rev Mod Phys 39, 78-124] and measured by us were observed.

The determination of the efficiency of energy dispersive X-ray spectrometers by a new reference material.

A calibration procedure for the detection efficiency of energy dispersive X-ray spectrometers (EDS) used in combination with scanning electron microscopy (SEM) for standardless electron probe microanalysis (EPMA) is presented. The procedure is based on the comparison of X-ray spectra from a reference material (RM) measured with the EDS to be calibrated and a reference EDS. The RM is certified by the line intensities in the X-ray spectrum recorded with a reference EDS and by its composition. The calibration of the reference EDS is performed using synchrotron radiation at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt. Measurement of RM spectra and comparison of the specified line intensities enables a rapid efficiency calibration on most SEMs. The article reports on studies to prepare such a RM and on EDS calibration and proposes a methodology that could be implemented in current spectrometer software to enable the calibration with a minimum of operator assistance.