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High‐sensitivity XRF analyzer (OLIVIA) using a multi‐crystal pyrographite assembly to reduce the continuous background
Author(s) -
Cheburkin Andriy K.,
Shotyk William
Publication year - 1999
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/(sici)1097-4539(199905/06)28:3<145::aid-xrs329>3.0.co;2-8
Subject(s) - monochromator , spectrum analyzer , detector , optics , spectrometer , incoherent scatter , crystal (programming language) , scattering , beamline , detection limit , analytical chemistry (journal) , physics , materials science , chemistry , beam (structure) , wavelength , chromatography , computer science , programming language
A new, original XRF analyzer (OLIVIA) for measuring trace elements was constructed using a multi‐crystal pyrographite assembly (MPA) to reduce the continuous background and improve detection limits. OLIVIA consists of an x‐ray monochromator as the source of exciting radiation with an energy of 17.44 keV (Mo Kα) and an energy‐dispersive x‐ray spectrometer with an Si(Li) detector, rotating sample holder and MPA. The MPA functions as an x‐ray ‘bandpass filter’ and consists of 18 individual pyrographite crystals aligned like the staves of a barrel. The MPA is positioned between the sample and Si(Li) detector and shields the x‐ray detector from the unwanted lines of the x‐ray spectrum. In this study, the OLIVIA instrument was optimized to measure Pb in fossil plant material (peat). Specifically, the MPA was adjusted such that only the region of the x‐ray spectrum containing the lines of Pb and a few of other trace elements (Se, Br and Rb) are able to pass through the MPA and reach the detector for analysis. In contrast, the x‐ray lines of other elements and the coherent and incoherent scattering peaks cannot reach the detector because of incompatible Bragg angles. Using this ‘filter’ the intensity of coherent and incoherent scattering from the sample decreased by a factor of 400, and the lower limit of detection (LLD) for Pb in peat is ca six times lower than that with our previous XRF design (EMMA), which also uses a monochromatic x‐ray excitation beam. In fact, the OLIVIA instrument achieved an LLD for Pb of 0.1 ppm in a real sample of plant material (NIST SRM 1515 Apple Leaves), a value which is far superior to those with conventional, commercial XRF instruments. In addition to Pb, the LLD for Br and Rb were also significantly improved. While the main goal of the present study was to improve the LLD for Pb, the MPA can be adjusted to reduce the continuous background and improve the detection limits for any element from Z =22 (Ti) to 39 (Y) (K lines) and from Z =57 (La) to 92 (U) (L lines). Copyright © 1999 John Wiley & Sons, Ltd.