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

Tracor noran sili detector for acquiring xrf spectra

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TRACOR NORAN Si(Li) detector) for acquiring XRF spectra and texture maps. The instrument is fully controlled by a personal computer. The specimen is translated step by step across a user-defined grid pattern in the x-y-z stage
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660 D. Rammlmair et al. Specimen Energy dispersive detector J 1 J 2 2J Collimator X-ray source Primary beam [hkl] Diffracted and fluorescent beams x y Fig. 7.130. Schematics of microbeam X-ray mapping (Fig. 7.131). Grid patterns of any shape are possible, in order to match the scanned field to the area to be sampled, e.g., scans along a line, across rectan- gles or polygons in 1- µ m wide steps over an area of 100 mm by 100 mm wide. The current sample position under the beam spot is monitored with a video camera, and so the corner points of the sampled region are easily defined. Energy-Dispersive Spectroscopy and Data Acquisition Identification of spectral components in the secondary beam must take into account the following features: a low background of continuous radiation Fig. 7.131. The experimental setup of the X-ray scanning instrument
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Methodological Developments and Applications 661 100 50 Mn Cu 200 220 311 222 400 331 422 10 0 5 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 keV 9 8 7 6 rel. Intensity Fig. 7.132. Energy-dispersive X-ray spectrum from an AlMn 1% metal sheet sharp characteristic lines due to scattering from the primary beam sharp characteristic fluorescence lines from the specimen broad diffraction peaks from the specimen (Fig. 7.132) Absorption in air has to be considered for quantum energies E x < 3 keV. Hence, a helium atmosphere or an evacuated specimen chamber will be indispensable if light elements are to be detected by XRF or if materials with large lattice constants have to be studied by XRD. Very high quantum energies, on the other hand, are not adequate, since Bragg’s angles decrease unduly up to grazing incidence with hard X-rays. Then the spot size is ex- tremely foreshortened and spatial resolution is impaired. A high excitation of fluorescence lines is obtained with an overvoltage of the primary beam of about twice the energy of the characteristic lines of the elements to be de- tected. A good compromise is obtained for most samples with an angle of incidence of ϑ 1 45 and quantum energies of the primary beam between 8 keV and 15 keV. A comprehensive PC software package has been developed. One part con- tains the hardware control of the goniometer, the Eulerian cradle, the x-y-z sample stage and the proportional counter, as well as the EDS system. The other part has been developed for the graphical representation of measured pole figures and scanning data of selected sample areas. The experimental pole-figure data can be used for ODF analysis, irrespective of the chosen angular sampling grid and specimen symmetry, and for the calculation of av- erage tensorial material properties by using a dedicated ODF program [472].
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