Filtern
Dokumenttyp
- Zeitschriftenartikel (12)
- Beitrag zu einem Sammelband (1)
- Sonstiges (1)
Schlagworte
- Color X-ray camera (4)
- Synchrotron radiation (4)
- EPMA (2)
- Elemental analysis (2)
- Polycapillary optics (2)
- SEM (2)
- X-ray optics (2)
- X-ray tube (2)
- XRF (2)
- pnCCD (2)
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%.
Phoenician ivory objects (8th century B.C., Syria) from the collections of the Badisches Landesmuseum, Karlsruhe, Germany, have been studied with full field X-ray fluorescence microimaging, using synchrotron radiation (SR-FF-microXRF). The innovative Color X-ray Camera (CXC), a full-field detection device (SLcam), was used at the X-ray fluorescence beamline of the ANKA synchrotron facility (ANKA-FLUO, KIT, Karlsruhe, Germany) to noninvasively study trace metal distributions at the surface of the archeological ivory objects. The outstanding strength of the imaging technique with the CXC is the capability to record the full XRF spectrum with a spatial resolution of 48 µm on a zone of a size of 11.9 × 12.3 mm² (264 × 264 pixels). For each analyzed region, 69696 spectra were simultaneously recorded. The principal elements detected are P, Ca, and Sr, coming from the ivory material itself; Cu, characteristic of pigments; Fe and Pb, representing sediments or pigments; Mn, revealing deposited soil minerals; Ti, indicating restoration processes or correlated with Fe sediment traces; and Au, linked to a former gilding. This provides essential information for the assessment of the original appearance of the ivory carvings. The determined elemental maps specific of possible pigments are superimposed on one another to visualize their respective distributions and reconstruct the original polychromy and gilding. Reliable hypotheses for the reconstruction of the original polychromy of the carved ivories are postulated on this basis.
Compact pnCCD-based X-ray camera with high spatial and energy resolution: a color X-ray camera
(2011)
For many applications there is a requirement for nondestructive analytical investigation of the elemental distribution in a sample. With the improvement of X-ray optics and spectroscopic X-ray imagers, full field X-ray fluorescence (FF-XRF) methods are feasible. A new device for high-resolution X-ray imaging, an energy and spatial resolving X-ray camera, is presented. The basic idea behind this so-called 'color X-ray camera' (CXC) is to combine an energy dispersive array detector for X-rays, in this case a pnCCD, with polycapillary optics. Imaging is achieved using multiframe recording of the energy and the point of impact of single photons. The camera was tested using a laboratory 30 µm microfocus X-ray tube and synchrotron radiation from BESSY II at the BAMline facility. These experiments demonstrate the suitability of the camera for X-ray fluorescence analytics. The camera simultaneously records 69696 spectra with an energy resolution of 152 eV for manganese Kα with a spatial resolution of 50 µm over an imaging area of 12.7 × 12.7 mm². It is sensitive to photons in the energy region between 3 and 40 keV, limited by a 50 µm beryllium window, and the sensitive thickness of 450 µm of the chip. Online preview of the sample is possible as the software updates the sums of the counts for certain energy channel ranges during the measurement and displays 2-D false-color maps as well as spectra of selected regions. The complete data cube of 264 × 264 spectra is saved for further qualitative and quantitative processing.
A single-bounce capillary with an ellipsoidal shape has been used for two-step focusing in combination with a Fresnel zone plate (FZP). The FZP serves as a first microfocusing element and produces a demagnified micrometer image of the source, before the elliptical capillary makes a last final compression of the beam. With 15 keV X-rays from the European Synchrotron Radiation Facility BM5 bending magnet, the two-step demagnification system produced a focus of about 250 nm with a gain of more than 1000. The use of an ellipsoidal capillary as a micro-mirror under off-axis illumination using micro-prefocusing optics might open up new opportunities in nanofocusing developments.