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X-ray Fluorescence: The Basics

Analytical chemistry is built on the premise of acquiring information about the composition and structure of sample materials through rigorous testing. This may involve the application of mechanical loads or extremely high temperatures to monitor the way that matter reacts to specific stressors. Although, the method applied fundamentally depends upon the properties of interest. Assessing the chemical content and structure of materials, for instance, is typically carried out via spectroscopic methods like X-ray fluorescence (XRF).

What is Spectroscopy?

Spectroscopy refers to a diverse toolset used to analyze materials based on various emission spectra. In this context, emission spectra are defined as the signals emitted by molecules after they have interacted with electromagnetic radiation. Unlike microscopy which uses visible light and a series of objective lenses to magnify samples for visual inspection, spectroscopy involves the acquisition of specific wavelengths of interest. As the name may suggest, XRF spectroscopy is concerned with X-rays.

What are X-rays?

X-rays are a form of sub-visible radiation on the electromagnetic spectrum. Spanning a wavelength range of approximately 10 picometres (pm) up to a maximum 1 nanometre (nm), they occupy the region between extremely high energy gamma rays and ultraviolet (UV). There are many ways that X-radiation can be characterized, but the two categories most pertinent to XRF spectroscopy are primary and secondary X-rays.

Primary X-rays are those produced by the source and directed in a collimated beam onto the surface of a sample. Some of this is backscattered, while some is absorbed by physical matter. This occurs at the atomic level where electrons in orbit around nuclei absorb the energy of X-ray photons and become excited. Electrons orbit atoms in specific bands, but when they are excited, they may transition to higher orbitals.

What is X-ray Fluorescence?

Understanding the process from here requires a basic knowledge of complex quantum physics. In the simplest possible terms, after an electron transitions to a higher band, it leaves a vacancy in the lower orbital that must be filled. An electron from a higher orbital will drop down to fill this so-called hole, releasing energy to do so. The emission of light in this manner is known as fluorescence, and the emission of secondary X-rays is subsequently termed X-ray fluorescence. This is incredibly valuable to analytical chemistry as the secondary X-rays emitted by samples are characteristic of the elements present.

Understanding XRF Spectroscopy

Exciting samples with primary X-rays and acquiring the resulting X-ray fluorescence signals enables chemists to develop an accurate spectrum of sample composition. There are numerous ways this can be carried out, though the two primary techniques are known as energy dispersive X-ray fluorescence (EDXRF) and wavelength dispersive X-ray fluorescence (WDXRF). We aim to explore these further in future articles but, for now, the main difference is a matter of resolution.

Achieving a clear X-ray fluorescence spectrum requires a range of interconnected hardware, software, and best practices. At XRF Scientific, our primary focus is on elevating the sample preparation phase of your workflow. We offer critical flux agents and fusion equipment to help prepare samples that are clear of matrix defects and are as close to a homogenous representation of the original material as possible. If you would like to learn more, please feel free to contact a member of the XRF Scientific team today.