[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Alternatively the samples can be raster scanned using

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Alternatively, the samples can be raster-scanned using a piezo YZ assembly, spreading out the heatload over several successive scans. This experiment opens a new way toward possibilities of mapping intracellular distribution of drugs used at pharmacological doses. SXRF is complementary to confocal mi- croscopy or nuclear microprobe analysis, and brings missing information not accessible by any other technique. Finally, simultaneous chemical speciation by X-ray absorption spectroscopy and microanalysis of living cells are exciting perspectives under active investigation. Element Specific Tomography X-ray fluorescence computed microtomography (XFCMT) is a nondestruc- tive, noninvasive imaging method which was introduced over 9 years ago [74] and started to play an increasing role in microanalysis [75–77]. XFCMT is an excellent complementary technique to phase contrast imaging in that it offers the much-needed elemental sensitivity down to trace element concentrations with the same micron-sized spatial resolution. In order to retrieve the quan- titative 2D/3D elemental information at the end of the tomographic scan, reconstruction techniques are used as opposed to the direct imaging methods associated with 2D mapping. As it requires a pencil beam as its probe, syn- chrotron radiation fluorescence tomography expanded and became a precise
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492 A. Simionovici and P. Chevallier and relatively straightforward method of microanalysis only with the advent of third-generation synchrotron sources such as the ESRF, APS and SPRING 8 that provide high energy/high flux beams. In the following, we describe high precision experiments performed at the ID22 beamline of the ESRF on real samples featuring inhomogeneous elemen- tal distributions, from the fields of Earth and Space Sciences [78]. Depending on the desired resolution, either of the vertical or horizon- tal scanning geometries are used, with the associated detectors positioned vertically, respectively horizontally at 90 to the beam. The horizontal fo- cusing/scanning geometry exhibits a significant decrease in flux necessary to demagnify the rather large horizontal source size by closing down the beam- line horizontal slits but has a better spectral purity, as it features Rayleigh and Compton scattering a few tens of times less than the vertical geom- etry, thanks to the 90 angle between incident and outgoing photons in the orbit plane and the high degree of linear polarization in the horizontal plane. The two movements used for the tomographic scans are Z/Y (verti- cal/horizonatal, precision 0 . 1 µ m) and R Y /R Z (rotation around a horizona- tal/vertical axis, precision 0 . 001 ). The other movements ( X , R X , y ) are used to align the sample rotation axis in the beam. The sample is mounted on a Huber goniometer head which is prealigned on a visible microscope setup in order to bring its rotation axis perpendicular to the beam and to reduce precession of the tomographic rotation axis at the beam position.
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