X-ray spectroscopy

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X-ray fluorescence spectrometry An analytical method which can be used to determine the concentration of a wide range of chemical elements, using the intensity of their fluorescent X-rays. An X-ray beam is used to excite atoms in a sample; electrons near the nucleus emit secondary or fluorescent X-rays on reversion to their original states. Short-wavelength X-rays are sorted by diffraction in a pure analysing crystal of known d-spacing (see COVALENT RADIUS). Since nλ = 2d sinθ (see BRAGG EQUATION), θ can be set to a value and radiation detected for a unique wavelength characteristic of the element being analysed. The intensity of the radiation measured, relative to a standard, is proportional to the concentration of the element. It is an important technique in the geochemical analysis of rocks.

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X-ray fluorescence (XRF) The secondary X-ray emission that results when electrons from the outer orbitals of an atom fill vacant inner orbital positions originally created by X- or gamma-ray excitation. These X-rays are characteristic of excited atoms.

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X-ray spectrometer An instrument for measuring the secondary X-rays emitted when the inner electrons of an atom (W, Au, etc.) are activated by a primary hard X-ray beam. The content of nearly all elements with an atomic weight greater than that of sodium can be estimated.

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