We report recent advances in absolute x-ray wavelength metrology in the context of producing modern standard reference data. Primary standard x-ray wavelengths are typically measured with two-crystal (or more) diffraction spectrometers operated in dispersive and non-dispersive geometries, giving natural-line-width limited profiles with high resolution and accuracy. Such instruments have been in use for over a century; today the results can be made traceable to the definition of the SI (système internationale) meter by using diffraction crystals that have absolute lattice-spacing provenance through x-ray-optical interferometry. Recent advances in goniometry, innovation of electronic x-ray area detectors, and other in situ alignment and measurement methods now permit robust measurement and quantification of previously-elusive systematic uncertainties. This capability supports infrastructures like the NIST Standard Reference Data (SRD) programs and the International Initiative on X-ray Fundamental Parameters and their contributions to science and industry. Both data projects are further served through NIST programmatic collaboration of wavelength-dispersive and (complementary) energy-dispersive spectroscopic techniques, the latter employing superconducting transition-edge sensors. This combination can provide, among other things, new tabulations of less-intense x-ray lines that need to be identified in XRF (X-Ray Fluorescence) investigation of uncharacterized analytes. After delineating the NIST traceability chain for primary x-ray wavelength standards, this paper posits the new opportunities for x-ray reference data tabulation that modern methods now afford.
Radiation Physics and Chemistry
x-ray spectroscopy, wavelength metrology, standards, traceability, reference data