= Moseley's law
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{title2=$\sqrt{\nu}=a(Z-b)$}
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<Moseley's law> describes an approximately linear relation between the square root of a characteristic X-ray <frequency> and the <atomic number>: $\sqrt\nu=a(Z-b)$ for a specified line series. The constants depend on which transitions are compared; $b$ represents an effective screening correction rather than a universal number for every line.
<Henry Moseley> bombarded samples with <electrons> and measured their characteristic X-ray wavelengths using a crystal spectrometer. Plotting the corresponding square-root frequencies revealed a systematic ordering by nuclear charge, including gaps where elements were missing. This helped distinguish the physical <atomic number> from ordering by atomic <mass>. Different line series and departures from exact straightness contain additional atomic-structure information; the simple relation is not an exact description of all X-ray transitions.<Moseley and X Rays by University of Oxford Department of Physics>[Moseley's graph and The story of Moseley and X-rays: apparatus, K and L lines, integer ordering and departures from linearity]{ref}
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