XRF Principle: The Fundamentals of XRF
The traditional use of X-ray fluorescence analysis (XRF) has its roots in geology. Solid samples were the first sample types analyzed by X-rays. Over the years the applications expanded and nowadays the applications cover the analysis of alloys, various types of powder samples to liquid samples and filter material.

The principle of XRF

The effect of X-ray fluorescence is based on the excitation of atoms in the sample. A primary X-ray, typically generated in an X-ray tube, hits an inner shell electron of the atom and ejects the election from the atom. The open position is filled by an electron from a further outer shell and fluorescence radiation is emitted. The fluorescence energy is equal to the energy difference between the two election shells. Therefore, the energy of this radiation is characteristic for the atom and indicates, what atom is present in the sample.

As many atoms are present in the sample, it will emit various X-rays with different energy. In an energy-dispersive XRF instrument the fluorescence radiation is collected by a semi-conductor detector. The X-rays create signals in the detector, which are depending on the energy of the incoming radiation. The signals are collected in a multi-channel-analyzer.

This process handles each X-ray one by one but with a high speed. A detector of a modern XRF machine can handle 1 million counts per second. This makes it a quasi-simultaneous measurement. Even with a short measurement time, the spectrum can give sufficient information to calculate intensities, which can be used to determine the composition of the sample. Using a longer measurement time allows for better statistics resulting in better precision and better peak-to-background thus resulting in improved detection limits.

For a highly precise analysis of an element present in the sample minimum a few million counts should be collected. This is quite easy if the sample contains a high concentration of an element and the detector can handle a high count-rate, but will be more difficult if concentrations are low and detection system are only able to handle a low count rate.

This XRF principle video presents an easy-to-understand introduction into the physics and the technology of an XRF analyzer. You can find more detailed information by requesting the featured whitepapers below. They will give you additional information about X-ray fluorescence spectroscopy as well as the benefits of an advanced XRF spectrometer.
XRF Instruments

SPECTRO xSORT

  • Robust tool, analyzes most alloys in 2 seconds, and identifies alloys containing light elements in 7 seconds, standard calibration captures alloys and precious metals for 16 matrices with 46 elements
  • Instrument usually ready to measure within 10 seconds after switching on, offers simultaneous result storage in various formats at different destinations (USB drive, network, or printer)
  • Compliance testing and quick screening of non-metallic samples. Video-camera for exact sample positioning and documentation of measured spot.

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    XRF Handheld xSORT

SPECTRO XEPOS

  • Outstanding sensitivity leads to up to a factor 3 improved precision – the basis for high accuracy when analyzing minor to major element concentrations
  • Measure lower than ever: Adaptive excitation, advanced tube design and high-count throughput detection system result in significantly (typically a factor 3) lower limits of detection for a wide range of elements
  • Master the unknown: The Turboquant II software tool provides an unprecedented ability to analyze unknown samples, regardless if they are liquid, solid or powder – whether tree leaves, plastics, oil, granite or glass…

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SPECTROCUBE

  • Fastest in its class: Twice as fast as typical testing, high precision in as little as 15 seconds
  • Excels in scope and accuracy: One analysis, 30+ elements — including traces
  • Unparalleled ease-of-use: Just three simple steps to accurate results

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    SPECTROCUBE



SPECTRO MIDEX for Precious Metals Applications

  • The market recognized gold standard for element analysis of precious metals
  • Wide scope of > 30 elements backed by extensive factory calibrations providing the best accuracy for traces and majors
  • Up to a factor of 3 shorter measurement times: choose exceptional results at conventional measurement times, or conventional results at exceptional measurement times

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    SPECTRO MIDEX

SPECTRO MIDEX

  • Fast and non-destructive compliance screening with flexible spot sizes, from 0.1 to 4 mm
  • Element line scans and mappings: Get a qualitative elemental composition within minutes ‒ other micro-XRF instruments may require hours
  • Comprehensive suite with factory prepared calibrations for screening of plastics and composites and analysis of alloys

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    SPECTRO MIDEX

SPECTROSCOUT

  • Light weight and portable elemental analyzer for precious metal alloys; spot size is only 1 mm
  • Fast and on-site: Elemental analysis of rock, sediment and soil. Element range starting from Na, detection limits for relevant trace elements significantly lower compared to other portable and handheld XRF instruments.
  • At the production line: High productivity with application specific packages. Small footprint with high analytical power.

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    Portable ED-XRF Analyzer SPECTROSCOUT

White Papers

WP 5 Reasons to Upgrade XRF 

Five reasons for upgrading to a next-generation ED-XRF analyzer 

ED-XRF instruments have made amazing strides in recent years. Quantum leaps in several technologies are making users rethink what’s possible with a modern analyzer. This paper explains why an upgrade of your current analytical solution could become inevitable.

White Paper Mitigating Matrix Effect 

Mitigating Matrix Effects with Advanced Spectra-Handling Functionality When Using XRF for High-Accuracy Elemental Analysis 

Creating the right basis for consistently high-accuracy results requires additional spectra handling functionality to determine the correct net intensities of the measured spectra. This paper explains why this additional functionality is a critical aspect of overcoming matrix effects and ensuring those consistently high-accuracy results.

Whitepaper Polymer 

X-ray Fluorescence Analysis of Polymers 

This White Paper examines to what extent X-ray fluorescence analysis is an appropriate technique for the elemental analysis of polymers. It also takes a close look on the sample preparation.

The Relevance of XRF Sample Preparation

Traditionally XRF is known to be non-destructive but this not always the case and the sample preparation has to be selected according to the analytical goal. The selected sample prep also depends on the sample type and is certainly different for alloys, granulates, powders or liquid samples.

Typical sample prep options are: 
No sample prep, Filling small particles, powder, liquids,… into XRF sample cups, Cleaning of sample surface, Removing of sample surfaces like oxide or coating layers, Machining or polishing of metal alloy surfaces, Pulverization of samples and filling the powder into XRF sample cups, Pulverization of samples, blending the powder with binder to prepare a pressed powder pellet, Preparation of pressed powder pellets from fine powder without binder (typically into Al-cups or steel rings, Preparation of fused beads, mainly from oxidic samples after blending with flux etc.

Why is sample preparation important?
The reason is that depending of the energy of the X-rays, the depth from which we can collect the fluorescence radiation can be rather small. In addition, this effect is also matrix specific. Generally speaking: The heavier the sample matrix, the lower is the penetration depth.
To get an estimate of this effect, commonly the so called “attenuation length” is calculated. This is the thickness from which the fluorescence signal is suppressed with a factor of 1/e. The following diagram shows the attenuation length for different elements in a pure polymer matrix with the assumption of an angle of 45 degrees between sample and detector.

Depending on the analytical requirements this means that a suitable sample preparation technology must be selected. An accurate analysis of the P content cannot be done from a polymer granulate. An accurate analysis of major elements in geological samples is typically done based on fused beads. For screening applications like compliance tests larger errors may be tolerated and therefore, liitle or no sample prep is chosen.

More information can be found on the SPECTRO XRF Overview page.