X-ray fluorescence analysis

Spectrometer Spectrometer

X-ray fluorescence analysis (XRD) is one of the modern spectroscopic methods for studying a substance in order to obtain its elemental composition, that is, its elemental analysis . Using it, various elements can be found from beryllium (Be) to uranium (U). The X-ray powder diffraction method is based on the collection and subsequent analysis of the spectrum arising from the irradiation of the test material with x-ray radiation . When interacting with high-energy photons, the atoms of a substance go into an excited state, which manifests itself in the form of a transition of electrons from lower orbitals to higher energy levels up to ionization of the atom. In an excited state, the atom abides for an extremely short time, of the order of one microsecond, after which it returns to a calm position (ground state). In this case, the electrons from the outer shells fill the vacant spots, and the excess energy is either emitted as a photon, or the energy is transferred to another electron from the outer shells ( Auger electron ) ^{[ specify ]} . In addition, each atom emits a photon with an energy of a strictly defined value, for example, iron when irradiated with X-rays emits photons Kα = 6.4 keV. Further, according to the energy and the number of quanta, they judge the structure of matter.

As a radiation source, both x-ray tubes and isotopes of any elements can be used. Since each country has its own requirements for the import and export of emitting isotopes, in the production of X-ray fluorescence technology, they have recently been trying to use, as a rule, an X-ray tube. The tubes can be either with a rhodium or copper , molybdenum , silver or other anode . The tube anode, in some cases, is selected depending on the type of task (elements requiring analysis) for which this device will be used. For different groups of elements, different values ​​of current and voltage on the tube are used. To study light elements, it is enough to set the voltage to 10 kV, for medium 20-30 kV, for heavy - 40-50 kV. In addition, in the study of light elements, the atmosphere has a great influence on the spectrum; therefore, the chamber with the sample is either vacuumized or filled with helium . After excitation, the spectrum is recorded on a special detector. The better the spectral resolution of the detector, the more accurately it will be able to separate photons from different elements from each other, which in turn will affect the accuracy of the device itself. Currently ^{[ when? ] The} best possible resolution of the detector is 123 eV.

After hitting the detector, the photon is converted into a voltage pulse, which in turn is counted by the counting electronics and finally transmitted to the computer. Below is an example of a spectrum obtained by analyzing a corundum mortar (Al ₂ O ₃ content is more than 98%, Ca , Ti concentration is about 0.05%). From the peaks of the obtained spectrum, it is possible to qualitatively determine which elements are present in the sample. To obtain an accurate quantitative content, it is necessary to process the obtained spectrum using a special calibration program (quantitative calibration of the instrument). The calibration program must be preliminarily created using standard samples whose elemental composition is precisely known. Simplified, in a quantitative analysis, the spectrum of an unknown substance is compared with the spectra obtained by irradiating standard samples, thus obtaining information on the quantitative composition of the substance.

X-ray fluorescence method is widely used in industry, scientific laboratories. Due to simplicity, the possibility of rapid analysis, accuracy, the absence of complex sample preparation, the scope of its application continues to expand.