Full-Field MXRF
the image slices, a method introduced by Radtke et al. [ 5 ]. In general the synchrotron beam can be collimated into a sheet beam vertically and horizontally by slit systems. In their study two different geometries were tested. A sidewards positioning of the camera did not provide optimal flux on the sample. By positioning the camera horizontal looking down on the sample, higher flux was obtained because in such geometry the second multilayer of the double multilayer monochromator (DMM) can be bent to focus and generate an excitation beam of 50 µm height. Figure 8 shows an example of a hornet imaged with a sheet beam. The specimen was chosen because insects are often used as biomonitors of metal contamination in the environment. An animation of the three-dimensional distributions in this image can be found in the supporting material of [ 5 ]. Data from 200 layers, corresponding to about 6 ms per voxel, were measured. The total measurement time was about 24 hours.
Absorption near-edge structure . In synchrotron-
Figure 7 : Shadows on a Cu plate caused by roughness and particles recorded in total refl ection geometry with an SLcam ® color X-ray camera. Reprinted from [ 6 ] with permission from Elsevier.
Shading is also observed in the drying droplets shown
in Figure 2 . Changing shading patterns (blue dotted lines) are caused by the changing physical shape of the specimen recorded in the drying experiments of droplets. Shadows are clearly visible, and they change in dimensions during the drying process.
Reconstructing 3D images from sheet-beam slices . Three-dimensional imaging can be achieved with full-field XRF by slicing the object with a sheet beam and reconstructing
based full-fi eld emission XANES microscopy, a narrow energy range on the excitation side, ΔE less than 1 eV, may be achieved using crystal monochromators. T e absorp- tion near-edge (XANES) features of one selected elemental fl uorescence line can be imaged. T is type of analysis can provide information on the distribution of a specifi c species of an element because the near-edge fi ne structure changes for diff erent chemical species of the regarded element. Although laboratory XANES point analysis has become quite powerful, XANES imaging suff ers from low intensity of the analytical signal. Synchrotron sources can provide a small Δ E, effi cient imaging optics, and now the color X-ray camera, SLcam ®
.
Full-fi eld fl uorescence mode micro-XANES was demonstrated recently by Tack et al. [ 13 ]. Figure 9 shows diff erential imaging of Fe 0 and Fe 3+ in an iron test sample containing both Fe foil and Fe 2 O 3 powder.
Figure 8 : Elemental images of a hornet acquired with full-fi eld XRF microscopy, sheet beam excitation, and an SLcam ® color X-ray camera. This shows the left of the reconstruction of the surface and a look inside the sample from the scatter signal. Color images show the distribution of elements in the 53rd layer with a resolution of (50 × 50) μ m2. Additionally the scattered intensity and the total deposited energy per pixel are shown. The deposited energy is equivalent to the measurement with a conventional CCD without energy resolution. Reprinted from [ 5 ] with permission from the Royal Chemical Society.
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