How to find the right XRF instrument for your application: the most important criteria for the perfect instrument configuration

The detector captures the fluorescence radiation emitted by the measurement object and largely determines which measurement tasks can be performed with the XRF instrument.

Ideal for: Comparatively simple coating thickness measurements in the range of approximately 0.1 µm to 50 µm, depending on the coating system.

Advantages: Thanks to its large active detector area and slightly curved window, a high proportion of the fluorescence radiation can be captured by the detector. This is particularly advantageous when a measurement distance between approximately 20 mm and 80 mm is required.

In addition, a proportional counter tube is less sensitive to deviations in sample alignment, adjustment of the measurement distance and sample geometry.

Ideal for: More demanding coating thickness measurements as well as material analysis.

Advantages: Offers significantly higher energy resolution than a proportional counter tube. A somewhat longer measurement time may be required for very small measurement spots.

Ideal for: Extremely thin layers down to the nanometer range, complex multilayer applications and highly precise material analyses.

Advantages: Offers the highest performance and best energy resolution of the detector types described here. The measurement range described extends from sodium under vacuum conditions to uranium. For elements present only in low concentrations, detection limits in the parts-per-million (ppm) range are possible.

The X-ray optics limit the cross-section of the primary beam and define the measurement spot size on the sample. As a general rule: For precise measurements, the measurement area should always be larger than the measurement spot. If the sample geometry permits, the measurement spot should be selected as large as possible for optimum precision. For cylindrical parts, for example, the sample diameter should be approximately four times the measurement spot diameter.

• Allow measurement spot sizes from several millimeters down to approximately 100 µm, depending on the measurement distance.
• Please note: The smaller the collimator, the less primary X-ray radiation reaches the sample, which weakens the fluorescence signal.

• Allow tiny measurement spots down to approximately 10 µm.
• They consist of hundreds of microscopically fine glass capillaries that are drawn into a defined shape and then bundled. Polycapillary optics can focus a large proportion of the primary radiation onto a tiny point and are therefore frequently used in the electronics and semiconductor industries to measure delicate structures.

The geometry of your samples determines the optimum measurement direction:

• Allows measurement of samples with heights of up to 80 mm as well as components with recesses.
• A laser pointer supports precise positioning of the sample.
• A programmable XY stage enables rapid movement between different measurement points on multiple samples and also allows semi-automation of your measurements.

• Ideal for flat samples such as sheets, coins, jewelry or precious-metal bars.
• Measurement distances of up to 35 mm can be achieved without difficulty.

• Handheld XRF instruments enable measurements on large, bulky parts such as aircraft carriers, turbine blades or pipelines.

The measurement environment influences which elements can be analyzed and which detection limits can be achieved.

Air is the simplest and most cost-effective measurement environment and is suitable for the vast majority of applications. However, scattering and absorption of the fluorescence radiation can occur in air. For most heavy elements, air absorption can be neglected.

For light elements (e.g. aluminum or silicon), the ambient air absorbs a large proportion of the signal radiation. A helium purge or evacuation of the measurement chamber drastically improves the signal-to-noise ratio, noticeably lowers the detection limits compared with measurements in air, and thus optimizes measurement precision.

Every measurement task has its own specific requirements for measurement technology. Which combination of detector, optics and measurement environment is right for you? The following table provides quick guidance for practical applications:

The correct configuration of your measuring instrument should always be selected based on the sample, measurement geometry, required measurement spot size, coating system, measurement mode and required detection limit.

To optimally tailor your future XRF instrument to your measurement task, we recommend clarifying the following questions together with our FISCHER experts:

• What type of sample is to be measured?
  Consider the material, size, geometry and surface condition of the sample.
• What is to be measured?
  Determine whether a coating thickness measurement, elemental analysis, or both are required.
• What coating thickness range is required?
  The required coating thickness range influences the selection of the detector and the configuration of the XRF instrument.
• How large does the measurement spot need to be?
  Small or complex measurement areas may require a microfocus X-ray tube, collimators or polycapillary optics.
• Which elements must be detected?
  The element range and required detection limit influence the excitation conditions and measurement environment.
• Is a specific measurement direction required?
  Measurement from top to bottom, bottom to top, or flexible measurement directions are suitable for different sample geometries.
• Is air sufficient as the measurement environment?
  For light elements, a helium purge or vacuum can improve measurement performance.