XRF: X-Ray Fluorescence Technology for Analysis of Metals & Alloys

How to Determine the Exact Composition of Any Metal & Alloy Materials Easily and in Mere Seconds

A Bruker XRF Analyzer

XRF analysis is an easy and accurate way finding out what chemical elements make up a material. X-ray fluorescence (XRF) technology has grown over the past sixty years. At first, XRF analysis was performed manually and inconveniently. It was mostly used in academic labs and was just starting to enter industry. Today, XRF analysis is the job of a small, handheld, automatic XRF “gun,” and you get professional results in seconds. Contact Bruker Inc., the world’s top manufacturer of handheld XRF guns for industry! Find out quickly how use XRF analysis for your industry and business. You can request a free demo or a quote!

This post offers an overview XRF analysis. Our further posts will discuss many specific applications of XRF for the metal industries. The most important technological improvement has been the diminishing size of XRF equipment. You will still see big XRF machines are in labs today. They are used when extra precision is a must. But most XRF analysis is now done on location by much smaller, portable and handheld XRF analyzers. One of the best and most famous among them is the Bruker S1 Titan™. It weights just 1.5 kg or 3.3 lbs, with battery. Material no longer needs to travel to a lab for analysis. Instead, the light-weight XRF analyzer does the job right at your location. Bruker is known as the market leader in handheld XRF. Our tools serve metal and alloy analysis, precious metal testing (such as gold and silver purity testing), Positive Material Identification (PMI), and Non-Destructive Testing (NDT), geological exploration and mining, product testing, electronic scrap testing, HAZMAT analysis, toxic soil testing, archaeology, art material analysis, and many types of material testing. Feel free to let us your metal or alloy analysis needs to find out whether handheld XRF is the right solution.

Why Choose Handheld XRF?

Although limited to the chemical elements in the Magnesium-Uranium range, Bruker’s XRF guns work great for a great many testing material needs in science and industry. Here are some of the main reasons why more and more professionals choose handheld XRF:

• It tests for many elements (from Magnesium through Uranium) all at once;
• Professional accuracy;
• Lightning speed (testing takes seconds);
• Nondestructive: the tested sample is 100% unchanged by analysis;
• Highly portable and light weight;
• Point-and-test on location;
• Highly automated operation;
• Easy to handle and use;
• Only minimal training is needed;
• Safe (contains no radioactive source);
• Very little sample preparation, very few restrictions (no tricky sample mechanisms, no vacuum chambers);
• The instrument’s classy and modern look-and-feel.

There is a problem with XRF analysis: it cannot detect carbon. For that reason, other types of tools work better for some types of organic material testing. Still, XRF is the best option for a great many types of inorganic analysis. There are other types of analysis, and some of them achieve similar results. All the same, XRF is often preferable to them either because it works better or because it offers better value or due to specific advantages. Let Bruker Inc. know your analysis needs. An expert will get back to you promptly.

How XRF Analysis Works

X-rays are a type of radiation with short wavelengths. They are located between the gamma radiation and ultraviolet parts of the spectrum. X-Rays can be used to measure both major and trace amounts of chemical elements found in alloys, minerals, soils, etc. When an X-ray source sends out high energy X-ray photons, those “primary” photons can excite “secondary” photons from the atomic structure of the material sample. These X-ray photons are called “fluorescent.” The process of their emission is known as “fluorescence.” Marked by a lower energy profile than the primary photons, such photons produce a characteristic spectrum that can be read by an XRF detector, revealing the elemental makeup of the sample. The specific energy of each element matches its concentration in the sample.

A little more technically, bombarding a material sample with X-Rays causes its ionization. When radiation energy is high enough to eject an inner shell electron from an atom, this destabilizes the atom as an outer shell electron takes up the place of the ejected inner shell electron. This happens with a flash of energy, because an inner shell electron is more tightly bound than an outer shell electron. The X-Ray Fluorescence (XRF) radiation produced in this way has a lower energy. The differences in energy among electron shells are fixed. For that reason, XRF radiation has a characteristic energy and can be used to detect and quantify the elements in the sample.

In theory, this method can be used to test for almost all chemical elements. However, in real life the range of elements is more limited. XRF analysis take place in earth’s atmosphere. The presence of air weakens the low-energy XRF radiation. This makes elements below silicon nearly undetectable. XRF analysis works best for elements measured from the K-line series whose absorption edges are just exceeded by the energy of the excitation source’s characteristic emission lines. This means the elements up to molybdenum in the Periodic Table. The K-series lines of the elements above molybdenum are difficult to excite with a high sensitivity, but they can be verified at a lower sensitivity.

How Deep Does XRF Analysis of Penetrate

The penetration depth of an XRF scan is the point under the surface of the scanned sample past which an element’s XRF line emission grows hard or impossible to detect, as it is absorbed by the material. This depth depends on the energy of the emitted characteristic XRF rays. Lower energies correspond to lower atomic numbers. Therefore, XRF penetration depth varies. It is between one and 10 mm for the higher atomic numbers. On the low end it is mere micrometers. The analyzed mass is usually between tens of milligrams and a gram. (This must be kept in mind when scanning materials with varied (heterogeneous) composition. For highly uniform materials such as alloys this is usually not an issue). Bruker’s XRF tools calculate averages for each element in the tested sample.

How Has XRF Changed over Time?

X-rays were first discovered by the German Wilhelm K. Röntgen. In 1901 he won the Nobel Prize in physics for his discovery. In 1909, the Englishman Charles Glover Barkla correlated X-ray radiation emitted by elements and with their atomic weights. This breakthrough marked the beginning of X-Ray spectroscopy. In 1913, Henry G. J. Moseley, another British scientist, used an X-ray instrument to accurately re-number the chemical elements in the Periodic Table. He showed that that the K-line transitions are displaced equally within an X-ray spectrum when the atomic number increases by one.

Röntgen used an ion tube as the source of X-Rays. Vacuum tubes did not come into use until later. An ion tube, filled with low-pressure air, bombarded a cold cathode with ions in a high voltage gas discharge to produce an electron emission. Accelerated from the cathode to the anode by an electric field, the electrons created an X-Ray flash. The original ion tubes were unstable and short-lived. They were replaced by the modern type of X-ray tube, also known as the Coolidge tube because it was invented by the American physicist William D. Coolidge. Filled with vacuum, such a tube generates electrons with the help of a hot wolfram filament. Today there are the many types of X-ray tubes. Bruker’s handheld XRF guns also rely on internal X-Ray tubes.

XRF analysis gained a place in labs in the 1950s. Further development focused on the technological components required of XRF tools, namely: XRF detectors, XRF radiation sources, and microprocessors.

Two Types of XRF Analysis: WDXRF vs. EDXRF

Early on, all XRF was wavelength-dispersive, which means that it was based on counting the number of X-rays of a specific wavelength diffracted by a crystal lattice. This process is called WDXRF for short (sometimes also WDX and WDS, with “s” standing for “spectrometry”). WDXRF tools test materials for specific elements. They are configured to detect the exact wavelengths of the corresponding emission lines, rather scanning scan over a broad spectrum all at once.

The more recent and more flexible XRF method is energy-dispersive XRF analysis (EDXRF for short, and sometimes also called EDX or EDS). EDXRF uses a silicon drift detector (SDD) with lithium-drifted silicon crystals. It can detect photons and read their energies. EDXRF analysis tools can test for most chemical elements. They boast low limits of detection (LOD). All of Bruker’s portable and handheld XRF analyzers are based on EDXRF. “Portable XRF” was first created for testing environments where the test object could not be moved or transported to a lab. But now the comfort and precision of handheld testing have made it the method most often used. You can perform XRF scans just about anywhere: just point the XRF gun at the object and run a test. Sample preparation is none to very little in most cases. Today, bulky and heavy lab instruments are reserved only for extra demanding, extra high precision analysis. Bruker’s handheld XRF tools approach lab-level accuracy and reliability. Our XRF guns are exact enough to determine material composition for most purposes or check for compliance with standards and norms.

A New Breakthrough: The Miniature X-Ray Tube

In the early days of XRF analysis, those big and unwieldy machines came equipped with an inside source of radiation. The instrument would flood the test sample with X-ray photons from the source. Natural or artificial radioactive isotopes were the first sources X-ray radiation for material analysis. They offered such advantages radiation constancy, independence of external power sources, compactness, and reasonable affordability. Their main advantage was portability. Their biggest problem with sealed source radiation was the associated health hazard. This imposed many use and storage restrictions. Only a handful of radioactive source types had acceptable decay patterns. These problems were slowing down the progress of portability. However, things have changed. Today, instead of embedded radiation, Bruker’s XRF analysis guns come fitted with small internal X-ray tube. This gives the miniaturized X-ray tube some important advantages, such as:

• No more worries about health hazards.
• No more regular source replacement due to its finite half-life.
• No wore worries about heavy legal regulations associated with radioactive materials, including obligatory registration, special licenses, special care and use requirements. (X-Ray tubes have their own safety requirements, but they apply only when a tube is in use).
• Greater brightness. (A fixed radiation source requires shielding. This limits brightness. An X-ray tube is brighter.)
• Better optimization.
• Better excitation of elements with low atomic numbers.

The Evolution of XRF Detectors

A Bruker XRF Analyzer

The 1970s introduced the noncryogenic, semiconductor based Si(Li) detectors. This was a big step in the advancement of XRF analysis. Before, an XRF analyzer machine would use a liquid nitrogen cryostat. Now this was no longer necessary. The Si(PIN) detector – the best among the new detector types that were invented in that era – still runs in the Bruker S1 TITAN™ model 300, the most affordable of our TITAN™ products. The next major development, the Silicon Drift Detectors, came in 1983. Being a solid state XRF detectors, the SDD scans the energy of a detected X-ray photon by the ionization that it causes within the detector. The big news here is the new detector material: a highly pure Si wafer with an extremely low leakage current. (Thanks to this, one-stage Peltier cooling is enough for the job.) A set of ring electrodes produces a transversal field, causing the charge carriers to “drift” to a small collection electrode. The introduction of the SDD resulted in improved count rates. Lastly, Bruker’s S1 Titan models 800 and 600 use our most current and cutting-edge large area CUBE™ SDD detector, enabling top performance and the lowest LoDs.