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Metrology

What Is X-ray Fluorescence, and How Does It Work?

Identify trace elements and alloys, analyze precious metals, and determine coating weight and plating thickness

Published: Tuesday, November 23, 2021 - 12:03

X-ray fluorescence (XRF) is an analytic method used to define the elemental structure of a material. Companies use specific XRF instruments when determining the chemistry for a sample of a material. How is this done? The machine measures the secondary or fluorescent X-ray that is released after being stimulated by the primary X-ray source.

Every component in any given sample makes its own set of characteristic fluorescent X-rays that are as individual as a human fingerprint. That is why spectroscopy designed specifically for X-ray fluorescence is ideal for generating both a quantitative and qualitative examination. Another major benefit of XRF is that it’s a nondestructive technique.

The X-ray fluorescence process can be segmented into phases. They are as follows:
• A high-energy X-ray is emitted from a controlled X-ray conduit. The X-rays irradiate the sample, whether it’s liquid or solid.
• When there is an X-ray with energy sufficiency more than the atom’s (K or L) shell-binding energy, an electron is displaced from one of the inner orbital shells within the atom.
• An electron from a higher-energy orbital shell in the atom fills the opening that was left behind, and the atom then regains stability.
• When a fluorescent X-ray is released, the electron descends into a lower state of energy.

How does X-ray fluorescence work?

As an X-ray XRF device starts a measurement, the X-ray tube emits high-energy radiation, which is also called the “primary” radiation. When these X-rays hit an atom in the sample, they add energy—i. e., they “excite” it, causing the atom to eject an electron close to its nucleus, a process known as “ionization.” Because this state is unstable, an electron from a higher shell moves in to fill the gap, thereby emitting “fluorescence” radiation.

The energy level of this secondary radiation is like a fingerprint: It’s characteristic for the respective element. A detector sees the fluorescence and digitizes the signal. After the signal has been processed, the device creates a spectrum. The energy level of the detected photons is plotted on the x-axis and their frequency on the y-axis (i.e., their count rate). The elements in the sample can be identified from the positions along the x-axis of the peaks in the spectrum. The levels along the y-axis of these peaks provide information about the elements’ concentration.

Why use XRF? What are the advantages? First, this simple sample preparation is safe. There’s no hazardous chemical waste left behind. It’s also quick and can analyze samples at the production site. There’s no need for daily recalibration because XRF analyses are highly accurate. Best of all, the analytical technique is nondestructive to the materials being sampled.

How is XRF used in various industries?

XRF analyzers typically are handheld instruments. They help industry professionals measure a variety of things, such as detecting quality and elements of scientific investigations. They detect trace elements, identify various alloys, and analyze precious metals. XRF analyzers also help determine the weight and plating thickness in coatings and deliver geochemical data to ensure that specific material-chemistry criteria are met.

Here’s how XRF analyzers can be helpful for certain industrial applications:

Recycling of precious metals: Determines accurate measurements of the grade of precious metals for reuse and prevents nonrecyclable metals from entering the recycling process.

Scrap metal recycling: Quick and precise sorting of various scrap metals for improved workflow efficiency.

Gas and oil: Helps identify positive material identification (PMI) of pipe material. This is an essential task where sulfidic corrosion is a concern in certain areas.

Metal fabrication: Analyzes elements to ensure no incorrect metals or alloys enter the manufacturing process of metal fabrication without destroying the material.

Aerospace and automotive: Ensures quality control when inspecting coated and metallic parts.

Environmental engineering, construction, and mining: Aids in risk assessment of hazardous sites, identifies viable resources, and helps in quality control.

Is XRF testing of samples safe?

Because an XRF analyzer emits a controlled radiation beam when the tubing mechanism is energized, reasonable efforts should be made to reduce the chances of radiation exposure. In many industries, this radiation safety standard is commonly known as the ALARA (as low as reasonably achievable) principle.

Three key factors will help minimize workers’ radiation exposure during XRF analyses sessions: time, distance, and shielding.

Fortunately, the radiation levels emitted from a handheld XRF analyzer are very close to the radiation exposure of a standard medical or dental X-ray device. However, caution should always take precedence. Always point the XRF device directly at the sample and never at a person or any part of the human body.

Here are some key safety tips to keep in mind for general X-ray radiation exposure:
• Ensure that all X-ray device operators receive proper training.
• Handle the device with caution. Be aware of the location of the primary beam indicator lights. Never aim the device at yourself or others, especially when the primary beam lights are illuminated, indicating that the device is on.
• Do not hold samples during analysis.
• Store all X-ray devices in a secure place when not in use, and obey local storage requirement laws.
• If you have a safety emergency with the device, notify your radiation safety officer (RSO) and analyzer vendor as soon as possible.

Where to find X-ray XRF fluorescence instruments

FISCHERSCOPE X-rays have provided reliable and quality testing for many industries since 1983. Their instruments are ideal for the contact-free measurement of coating thickness, nondestructive material analysis, and more. In addition, they are well-known in the industry for their precision, accuracy, and durability.

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About The Author

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Dan Hamilton

Dan Hamilton is the content manager at Helmut Fischer Technologies. He started his career at Helmut Fischer in 2019, focusing on the high-quality products and services being offered. His unwavering passion for content has helped deliver the highest quality of content to the Helmut Fischer website.