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| X-ray fluorescence | |
|---|---|
| Name | X-ray fluorescence |
| Invented by | Wilhelm Röntgen (discovery of X-rays), Henry Moseley (atomic number studies), Sir William Bragg (X-ray crystallography influences) |
| Year | 1895 |
| Fields | Physics, Chemistry, Materials science |
| Applications | Archaeology, Art conservation, Geology, Forensics, Environmental science |
X-ray fluorescence is an analytical spectroscopic technique that determines elemental composition by measuring secondary X-rays emitted from matter excited by a primary X-ray source. Developed through contributions by Wilhelm Röntgen, Henry Moseley, and contemporaries in Cambridge, the method underpins modern investigations in Archaeology, Geology, Materials science, Art conservation, and Forensics. Instruments range from laboratory-based wavelength-dispersive and energy-dispersive systems to portable units used at Smithsonian Institution field projects and United Nations environmental assessments.
X-ray fluorescence (XRF) arises when incident X-rays displace inner-shell electrons producing characteristic emission; detection of these emissions yields qualitative and quantitative elemental information. Historical milestones include early laboratory observations in Paris, systematic atomic number correlations by Henry Moseley at the University of Oxford, and later commercial instrument development by firms in Germany and United States. Contemporary practice intersects standards set by International Organization for Standardization, protocols from United States Environmental Protection Agency, and museum guidelines from institutions such as the British Museum.
Core physics involves photoelectric absorption and subsequent electronic transitions between atomic shells, governed by quantum mechanics developed in contexts like Bohr model debates and later refined through work at Cavendish Laboratory and Institut Pasteur-era spectroscopy. Characteristic lines (K, L, M) correspond to transitions such as L→K and M→L; their energies scale with atomic number as elucidated by Henry Moseley and interpreted using theories advanced at Max Planck Institute. Secondary processes include Auger electron emission and elastic/inelastic scattering, the latter described in studies at CERN and Lawrence Berkeley National Laboratory. Interaction volumes and fluorescence yields depend on density, atomic composition, and incident beam energy, factors considered in instrument design at Massachusetts Institute of Technology and Stanford University.
Major instrument classes include energy-dispersive XRF (EDXRF) and wavelength-dispersive XRF (WDXRF). EDXRF systems often employ semiconductor detectors developed from technologies at Bell Labs and Oak Ridge National Laboratory, while WDXRF uses crystal analyzers informed by work at Royal Institution and Daresbury Laboratory. Synchrotron radiation facilities like European Synchrotron Radiation Facility and Argonne National Laboratory provide high-brightness excitation for micro-XRF mapping, paralleling portable analyzers used by field teams from Smithsonian Institution or UNESCO. Ancillary components—X-ray tubes, radioisotope sources such as Americium-241, monochromators, and detectors like silicon drift detectors—reflect innovation traced to General Electric and national laboratories.
XRF supports provenance studies at museums like the Louvre and Metropolitan Museum of Art, quality control in industries represented by Siemens and General Motors, mineral exploration conducted by companies with geologists from US Geological Survey, and environmental monitoring under programs of the European Commission. Archaeometric investigations tie analyses to sites such as Pompeii, Machu Picchu, and Çatalhöyük, while forensic labs associated with FBI and Scotland Yard employ XRF for trace evidence. Energy-sector applications include battery material characterization pursued by research groups at Toyota and Tesla.
Preparation ranges from minimal cleaning for non-destructive museum work at institutions like the Victoria and Albert Museum to pressed pellet formation and fusion bead creation in industrial labs such as those at Bureau Veritas and SGS. Thin films and coatings are characterized using standards developed in collaboration with National Institute of Standards and Technology and inter-laboratory comparisons coordinated by International Union of Crystallography. Micro-XRF mapping at synchrotrons often requires mounting on substrates used at Lawrence Livermore National Laboratory to minimize background. Calibration employs certified reference materials from NIST and round-robin tests overseen by bodies including International Atomic Energy Agency.
Quantification strategies include fundamental parameter methods, empirical calibration curves, and standardless approaches. Software packages trace intellectual lineage to academic groups at University of Oxford and ETH Zurich and commercial vendors associated with Bruker and Malvern Panalytical. Matrix corrections address absorption and enhancement effects following formalisms developed in studies at Imperial College London and University of California, Berkeley. Peak deconvolution, baseline subtraction, and limit-of-detection calculations draw on algorithms originating from work at Los Alamos National Laboratory and KTH Royal Institute of Technology.
Limitations include reduced sensitivity for elements lighter than sodium, spatial resolution constrained by beam size and interaction volume, and matrix effects that complicate quantification—issues studied at Max Planck Institute for Chemistry and Florida State University. Common error sources are surface contamination, sample heterogeneity encountered in excavations at Knossos, detector dead time reported by teams at CERN, and spectral interferences illustrated in case studies from Smithsonian Institution conservation labs. Regulatory and safety constraints involving ionizing radiation are managed under frameworks from International Commission on Radiological Protection and national agencies such as US Nuclear Regulatory Commission.
Category:Analytical techniques