X-rays are a part of the electromagnetic spectrum and are on the higher energy side of the ultraviolet rays. They are expressed in terms of their wavelength in nanometers (nm) or their energy in kilo electron volts (keV). X-ray fluorescence (XRF) can be used to essentially analyze elements from sodium to uranium, in concentrations that vary from parts per million to higher percentages, in liquids, solids, and powders.
How Does X-Ray Fluorescence Work?
Two important components are equipped in all the XRF instruments: an X-ray source (usually an X-ray tube) and a detector. The source generates the primary x-rays that are directed at the surface of a sample. The rays at times pass through a filter for modification of the X-ray beam. When the atoms in the sample are hit by the beam, they react by producing secondary X-rays, which are then gathered and processed by the detector in the analyzer to generate a spectrum that shows the intensity peaks of the X-rays against their energy. The element can be identified by its peak energy. Its peak area, or intensity, indicates the amount of the element in the sample.
Subsequently, the analyzer uses this information to calculate the elemental composition of the sample. The entire process, from pushing a start button or a trigger to obtaining the analysis results, can be finished within 2 seconds, or it could take several minutes depending on the used instrument, the range of elements being measured, and the concentrations of the elements.
The energy of the emitted X-rays is characteristic of the element, which indicates that XRF provides qualitative information related to the sample being measured. Yet, XRF is also a quantitative method.
What Happens to the Atoms in the Sample During the Analysis?
A stable atom consists of a nucleus and electrons orbiting around it. The electrons occupy different energy levels or shells (such as K, L, M, N), where different energy levels can hold different numbers of electrons. When an atom is collided by a high-energy primary x-ray beam, its equilibrium is affected. An electron from a low energy level is ejected, thereby creating a vacancy and making the atom unstable. To reinstate the stability, an electron from a higher energy level takes the vacant place, and the excess energy liberated during movement of the electron between the two levels is emitted in the form of a secondary X-ray.
This information has been sourced, reviewed and adapted from materials provided by Hitachi High-Tech Analytical Science.
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