What Makes X-Ray Fluorescence Chemically-Specific?
X-ray fluorescence (XRF) is a non-invasive analytical method that is used to analyze the chemical and elemental composition of a wide range of materials. Traditionally, this method was used in Geology to determine the elemental makeup of rock, sediments, minerals and other earth samples, but its applications have now expanded.
What is X-Ray Fluorescence?
After a sample has been excited by a primary X-ray source, such as gamma or x-rays, it releases fluorescence. Fluorescence is the light that is emitted by certain materials after they have absorbed radiation. Still, it is important to understand that fluorescent material must emit light of a wavelength different from the one it absorbs. Once the light has been released, XRF analyzers are used to identify the chemical composition of a sample. Additionally, XRF analyzers can study a group of fluorescent X-rays that are unique to the specific element within the sample. A more in-depth understanding of X-ray fluorescence can be found in our previous blog post as we move on to look at what makes X-ray fluorescence chemically specific.
What Makes X-Ray Fluorescence Chemically-Specific?
Chemists and materials scientists routinely deploy XRF spectroscopy to determine a sample’s chemical fingerprint. The term “fingerprint” is used as it adequately describes how XRF spectral data is a unique identifier of a sample’s specific chemical makeup. How and why this is the case requires a cursory understanding of particle physics and quantum mechanics.
All chemical elements are comprised of atoms; the smallest unit of matter. But atoms are themselves composed of subatomic particles that behave in distinct ways. There is always a central, positively-charged nucleus surrounded by one or more negatively charged electrons; protons or neutrons. These electrons orbit the nucleus in discrete spheres, or shells, which are described as higher or lower orbitals depending on their energy level. Higher energy electrons occupy higher orbitals and vice versa. When an inner electron absorbs enough energy, it may be expelled, forming what is known as a core hole. In order to rectify this instability, electrons from higher orbits “fall” to fill the “gap”. But dropping from one shell to another requires a loss of energy. Thus, when electrons fall from higher orbitals to fill core holes, they emit radiation in the form of fluorescence; the energy of which is equal to the difference between the two orbitals. This is key, because these signals are intrinsic, meaning each chemical element has its unique signal.
This is an extremely simplified explanation of the mechanics at play within X-ray fluorescence, but it should suffice to explain how XRF spectrometers provide extreme specificity when it comes to chemical fingerprinting. The detector obtains the extremely weak emission spectra of a sample struck with an X-ray beam, yielding a spectrum of peaks and troughs that denote the specific elements present in the sample. This is how analysts can precisely determine the composition of various samples down to the sub-parts per million (ppm) range.
XRF Scientific
XRF Scientific is an experienced supplier of a range of instruments and products that are required for X-ray fluorescence preparation and analysis. We can offer support regarding XRF spectroscopy and its applications, so if you are looking for more information on X-ray fluorescence, contact us today and we’ll be happy to help.
