Wilhelm Conrad Rontgen, a German physicist, won the very first Nobel Prize in physics in 1901 after he discovered the X-rays back in 1895. The new technology was swiftly used by other researchers and doctors as per the SLAC National Accelerator Laboratory.
Charles Barkla, a British physicist, carried out research between 1906 between 1908 and 1906 which led him to discover that X-rays might be a distinctive of particular substances. His work also won him the Nobel Prize in physics, however, it was not until 1917 that he received the prize.
The application of X-ray theoretic spectroscopy began earlier in 1912 with a father and son team composed of British physicists William Henry Bragg and William Lawrence Bragg. They employed spectroscopy in order to understand the ways in which X-ray radiation acted on crystal atoms. Their method, known as X-ray crystallography was adopted as the norm in the field in the year following and received the Nobel Prize in physics in 1915.
The X-rays comprise X-radiation, which is a type of electromagnetic radiation. The most common X-rays are those with a wavelength of 0.01 up to 10 nanometers which corresponds to frequencies in the 30 petahertz range and 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies that are in the range of 100 eV to 100 keV, created by the deceleration and acceleration of electrons with high energy. The term “X-ray spectroscopy” is a generic term used to describe a variety of spectroscopic methods to characterize materials employing the excitation of x-rays.
X-Ray Spectroscopy Principle
XRF is a method that involves the interaction of electron beams as well as x-rays and samples. This is possible because of the behaviour of atoms as they are in contact with radiation. When materials are excited by short wavelength radiation with high energy (e.g. or radiation like X-rays) and they become Ionized. If an electron in the inside of an atom is stimulated by the radiation of a photon it is moved to a greater energy level.
In the event that it returns to the lower energy level the energy was previously gained through the excitation is released in an image with the wavelength that is typical for the particular element (there may be several distinct wavelengths for each element). Therefore, atomic X-rays are released when electronic transitions occur to inner shell states of the atoms with a low atomic number. They also have distinct energy levels that are related to the number of atoms, and every element also has an spectrum of X-rays which could be utilized to determine the element.
How X-ray spectroscopy works
The XRF spectrometer operates by observing that when a sample is illuminated by a powerful beam of X-rays, also known as an incident beam some of the energy gets scattered, however some of it is also absorbed by the specimen in a way that is dependent on the chemistry of the sample. The beam that is X-ray-intense is usually produced by a Rh target, however Cr, W, Mo and others may also be employed in accordance with the purpose.
When an x-ray strikes a an object, it emits the x-rays in a range of wavelengths that correspond to the type of atoms in the. If the sample contains a lot of elements The use of an Wavelength Dispersive Spectrometer can allow the division of a complicated emission X-ray spectrum into distinct wavelengths for every element that is present.
Different kinds of detectors are employed to measure the intensity of the emitted radiation. The amount of energy that is measured through these devices is proportional to amount of the element present in the sample. The precise value for every element is determined from previous analyses of different methods.
Instrumentation of X-Ray Spectroscopy
Components of X-ray spectroscopy:
- X-ray generating equipment (X-ray tube)
- Collimator
- Monochromators
- Detectors
A. X-ray generating equipment (X-ray tube)
X-rays can be produced through the X-ray tubes. It is a vacuum tube that utilizes an extremely high voltage to speed up the release of electrons by the cathode’s hot surface to a very high speed. The electrons of high velocity interact with a metal object and the anode. This creates the”X-rays.
B. Collimators
A collimator is a tool that reduces the size of a beam of waves or particles. The word “narrow” means to cause the motion directions to be more aligned in a particular direction (i.e. collimated, collimated, (or parallel). Collimation can be achieved through the use of parallel plates of metal or by the use of a tube bundle ,0.5 or smaller in diameter.
C. Monochromator
Monochromator crystals partially transform an unpolarized beam of X-rays. The principal function of the monochromator is to isolate and transmit a small part of optical signals from a greater spectrum of wavelengths that are available at the point of input.
Types of Monochromator
- Metallic Filter Type
- Diffraction grating type
D. X-ray Detectors
The most commonly employed detectors include:
- Solid State Detectors
- Scintillation Detectors
Solid State Detectors
The semiconductor’s charge carriers comprise holes and electrons. Radiation that strikes the semiconducting junction creates electron-hole pairs when it passes through it. The electrons as well as the holes get eliminated under the influence of an electric field. The appropriate electronics are able to collect the charge within the form of a pulse.
Scintillation detectors
Scintillation detectors comprise an instrument called a scintillator, and like PMT (Photomultiplier tubes) which converts the light into electrical signals.
- It is made up of an evacuated glass tube with the photocathode. It is typically composed of between 10 and 12 electrodes, referred to as Dynodes and an anode.
- The photocathode emits electrons that are attracted by the first diode and then accelerate to kinetic energies that are equal to the difference in potential between the photocathode and first diode.
- When electrons strike the first dynode five electrons are released from the dynode per electron that hits it.
- These electrons are attracted by the second dynode, then on to the anode.
- Total amplification of PMT is the result of the individual amplifications that occur at each Dynode.
- The amplifying can be controlled by altering the voltage that is applied by the PMT.
X-Ray Spectroscopy Applications
The X-Ray spectrometry technique is employed in a myriad of uses, which includes
- Industry of petroleum (e.g. sulfur content in crude oils as well as petroleum-related products)
- Environment studies (e.g. studies of particulate matter in air filters)
- Cement production
- Mining (e.g., monitoring the quality of the ore)
- Field analysis in environmental and geological studies (using handheld, hand-held XRF instruments)
- Research in the field of igneous, sedimentary metamorphic, and igneous petrology
- Soil surveys
- Manufacturing of glass and ceramic
- Metalurgy (e.g. Quality control)
X-Ray Spectroscopy Advantages
- If other methods of spectral analysis are unable to determine the chemical’s identity, Xray spectrum is the method to use for structural analysis with the other parameters, such as bond lengths and angles are also measured.
- The X-ray spectrum is an effective method of determining the structure of an element.
X-Ray Spectroscopy Limitations
- The majority of chemists find this process extremely tedious and time-consuming and requires a skilled hand.
- The process requires the presence of a compound in one crystal.
References
- Balci, Metin (2005). Basic 1H- and 13C-NMR Spectroscopy Volume 446 || Introduction. , (), 3–8. doi:10.1016/b978-044451811-8.50001-2
- Feng, X., Zhang, H. & Yu, P. (2020). X-ray fluorescence application in food, feed, and agricultural science: a critical review. Crit Rev Food Sci Nutr, 1-11.10.1080/10408398.2020.1776677
- Smyth, M. S. & Martin, J. H. (2000). x-ray crystallography. Mol Pathol, 53, 8-14.10.1136/mp.53.1.8
- Franklin, R. E. & Gosling, R. G. (1953). Molecular Configuration in Sodium Thymonucleate. Nature, 171, 740-741.https://doi.org/10.1038/171740a0
- https://www.iucr.org/__data/assets/pdf_file/0013/733/chap16.pdf
- https://www.azolifesciences.com/article/X-Ray-Spectroscopy-An-Overview.aspx
- http://instructor.physics.lsa.umich.edu/adv-labs/X-Ray_Spectroscopy/x_ray_spectroscopy_v2.pdf
- https://new.bhu.ac.in/Content/Syllabus/Syllabus_3006312820200416111005.pdf
- https://www.iaea.org/topics/x-ray-spectrometry
- http://www.issp.ac.ru/ebooks/books/open/X-Ray_Spectroscopy.pdf
- http://websites.umich.edu/~jphgroup/XAS_Course/Harbin/Lecture1.pdf
