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A researcher whose team used electron microscopy and X-ray spectroscopy to measure catalyst composition during gold-seeded gallium arsenide nanowire growth. Observing the catalyst while the wire grows addresses a central experimental difficulty: a particle examined after cooling need not preserve its working composition. Measuring the catalyst under growth conditions helps connect the supply of material to the liquid with the formation of new solid layers.^[ref]

Charles Barkla distinguished characteristic X-ray emission associated with a chemical element from radiation that varied more continuously with the exciting conditions. Comparisons of secondary radiation, absorption and emission showed that different chemical elements produce reproducible characteristic components. The emitting material therefore became an experimentally identifiable part of the spectrum. This work helped establish X-ray spectroscopy as a probe of atomic structure before a complete microscopic explanation of the characteristic lines was available.^[ref][ref]

A physicist.^[ref]

A contributor to international nomenclature recommendations for X-ray spectroscopy. The system relates line names to electronic energy levels instead of requiring a separate historical label for every transition, making complicated spectra easier to describe consistently.^[ref]

Henry Moseley measured characteristic X-ray frequencies across a sequence of chemical elements. For a given series, the square root of the frequency is approximately linear in atomic number after a screening offset is included. The regularity connects a spectral measurement with a discrete nuclear-charge label, rather than merely correlating with atomic weight. Missing positions in that sequence also made X-ray spectroscopy a way to test and extend the periodic ordering of chemical elements.^[ref]

A physicist.^[ref]

Hugo Atterling's scientific memoir of Manne Siegbahn explains how apparatus and source composition shaped early X-ray spectroscopy. One example traces two unexpected lines in a 1914 spectrum to a silver layer beneath a platinum coating, observed in first and second diffraction orders. The account connects identification of a chemical element with the interpretation of the instrument, rather than treating each observed line as a new property of the nominal target. His memoir also documents the development of precision and vacuum spectrometers.^[ref]

Physics.^[ref]

Manne Siegbahn developed precision X-ray spectroscopy for investigating atomic structure. A crystal converts an X-ray wavelength into a diffraction angle through Bragg's law. Careful control of the crystal geometry, angular calibration, spectral resolution and instrumental absorption therefore determines which characteristic spectral lines can be distinguished. His instrumentation resolved relationships and small differences that a coarser spectrometer would merge, making precision measurement part of the explanation of atomic X-ray spectral lines.^[ref]

Physics.^[ref]

Awarded to Karl Manne Georg Siegbahn for X-ray spectroscopy. He received the prize in 1925. The Siegbahn precision X-ray wavelength spectroscopy article describes its calibration problems.^[ref]

A scientific contributor to IUPAC recommendations that standardize names for X-ray spectroscopy. The proposed notation identifies emission lines and absorption edges through their underlying energy-level designations, making the physical transition easier to compare across measurements and publications.^[ref]

A contributor to a standardized notation for X-ray spectroscopy. Naming a line through the electronic levels involved reduces reliance on historical labels. The resulting nomenclature gives experimentalists a consistent way to communicate which atomic transition a measured feature represents.^[ref]

A supernova remnant is the expanding stellar debris and shocked surrounding gas left by a supernova. The debris drives an outward shock wave into the ambient interstellar medium; a reverse shock wave heats the ejecta as the expansion is decelerated. Hot plasma emits X-rays, while accelerated electrons produce synchrotron radiation in the magnetic field. Comparing successive images measures expansion, and X-ray spectroscopy maps the expelled chemical elements. In Cassiopeia A, the Chandra X-ray Observatory resolves the outer shock and heated debris. Such observations connect an explosion's kinetic energy and newly produced elements to the subsequent heating and enrichment of the interstellar medium.^[ref]

William Henry Bragg developed experimental methods that turned crystal diffraction into X-ray spectroscopy. A crystal selects reflected radiation at particular angles, while a movable detector measures the reflected intensity. Relating these peaks to lattice-plane spacing connects an instrument reading with the wavelength of the incident radiation. His joint work with Lawrence Bragg established a quantitative relation between crystal geometry and X-ray reflection, helping make diffraction a practical probe of both radiation and structure.^[ref]

A physicist who worked on crystal scattering and Bragg's law.

Institutional biography: www.rigb.org/explore-science/explore/person/william-henry-bragg-1862-1942