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- SEM (3)
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- XRF (2)
- Absolute X-ray spectrum (1)
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A calibrated instrumental setup was specially developed for the purposes of accurate measurements of absolute X-ray spectra emitted by modern micro-focus, low-power X-ray tubes. By knowing all the instrumental parameters the spectra measured with the 16 m long setup are recalculated into emitted X-ray tube spectra in photons per eV per msr per nA per s.
A model is discussed which describes the generation of X-rays in conventional tubes using tabulated bremsstrahlung energy spectra depending on three variables: the target atomic number, the incident electron kinetic energy, and the fraction of energy radiated. Additionally a parameter-free description of the characteristic radiation is included. The constructed model includes technical tube parameters like kilovoltage, target material, and angles of electron incidence and photon emission to also account for self-absorption in the target, as well as radiographic parameters like filtering. In order to verify model results, detector response is also considered. The validity of the proposed model is shown by measurements. Future work includes the extension of the model to transmission targets. This research was supported by the German Federal Ministry of Economics and Technology under contract MNPQ transfer II D 5-30/06.
Determination of the efficiency of an energy dispersive X-ray spectrometer up to 50 keV with a SEM
(2009)
Both electron and polychromatic photon excitations (micro-focus X-ray source) at a scanning electron microscope (SEM) are used to determine the efficiency of an energy dispersive X-ray spectrometer up to 50 keV by means of a calibrated X-ray spectrometer and reference materials (RM) specially selected for this purpose.
X-ray Fluorescence (XRF) with a scanning electron microscope (SEM) is a valuable completion of the analytical capabilities of SEMs. Small and compact micro-focus x-ray sources are mounted to the microscope chamber, and the x-ray spectra are monitored with conventional EDS systems. Up to now the x-ray tubes used for the micro-focus x-ray sources are equipped with beryllium windows about 100 µm thick. The poly-capillary x-ray lenses have their transmission maximum at photon energies around 10 keV. It drops down in both low- and high-energy ranges. Hence, L-radiation from an Mo or Rh target will be strongly attenuated, and the excitation of fluorescence in the soft x-ray range becomes very ineffective. A new micro-focus x-ray source was developed. It is characterised by a lower self-absorption in the tube target, thin beryllium windows and an x-ray optics having a large distance between its foci and the maximum of transmission at about 5 keV. Thus K line fluorescence of light elements becomes effectively excited by the L-radiation from Mo or Rh tube targets. The detection limit for sodium oxide in glass was found to be below 1 mass%.
Zusammenfassung
Der Prototyp einer Flachröntgenröhre mit einer maximalen Röntgenenergie von 240kV (600W) und einer Brennfleckgröße von 0,4 * 0,4 mm nach DIN EN 12543 wird vorgestellt. Das Design dieser Flachröntgenröhre mit geringer Aufbauhöhe ist in Metall-Keramik-Technik ausgeführt. Die Beschleunigungsstrecke Katode-Anode ist senkrecht zur Haubenachse ausgeführt. Die Röhre ist als bipolares System aufgebaut. Kleine Durchmesser der Hochspannungskabel verringern das Gewicht und resultierende Kraftmomente bei der manuellen Manipulation sowie beim Verfahren in einem mechanisierten System. Der Targetwinkel beträgt 6° und bewirkt eine höhere Brillianz der Röntgenstrahlung. Die Geometrie des Strahlenaustrittsfensters (Emissionsfenster) ist in Fächerstrahlgeometrie zur tomografischen Prüfung ausgelegt.