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Bent and flat highly oriented pyrolytic graphite crystals as small bragg angle monochromators in thin‐specimen energy‐dispersive XRF analysis
Author(s) -
Beckhoff Burkhard,
Laursen Jens
Publication year - 1994
Publication title -
x‐ray spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.447
H-Index - 45
eISSN - 1097-4539
pISSN - 0049-8246
DOI - 10.1002/xrs.1300230104
Subject(s) - bent molecular geometry , materials science , optics , pyrolytic carbon , beam (structure) , crystal (programming language) , monochromatic color , highly oriented pyrolytic graphite , bragg's law , intensity (physics) , curvature , graphite , diffraction , physics , geometry , chemistry , organic chemistry , mathematics , pyrolysis , computer science , composite material , programming language
A monochromatic high‐intensity x‐ray beam, obtained by Bragg reflection of the strongest characteristic tube line under small angles on single crystals, can be used as an EDXRF excitation source. A systematic selection procedure and search of 55 single crystals suitable as EDXRF Bragg reflectors was made and highly oriented pyrolytic graphite (HOPG) was found to be a superior candidate for the characteristic Kα line of an Mo tube within the range of low‐order reflections, yielding the highest intensities. Meridionally and sagitally curved HOPGs were studied in a flexible experimental set‐up and the reflected beam intensity and profile were compared with the corresponding data obtained from flat HOPGs with different mosaic spreads. The relationships between collimation, crystal curvature and mosaic spread were evaluated. The experimental angular beam acceptance and the secondary extinction effects dependent on the mosaic spread of the HOPG were found to be in line with theoretical expectations. Measured in similar configurations as required for realistic EDXRF applications, the sagitally bent HOPG increases the reflected beam intensity up to 77% whereas the meridionally bent HOPG yields an intensity gain of only up to 28% compared with the flat crystal with the same mosaic spread. The detection limits for the corresponding thin‐filter EDXRF analysis are presented.