Wavelength-Dispersive X-Ray Fluorescence Spectrometer

What is the Wavelength-Dispersive X-Ray Fluorescence Spectrometer?

A wavelength-dispersive XRF spectrometer uses analyzing crystals to diffract selected wavelengths for very high resolution. It is chosen for routine precise major-element and light-element analysis and for the lowest XRF trace detection limits.

Overview

In WDXRF the fluorescence from the sample strikes an analyzing crystal that diffracts only one wavelength at a time to a detector according to Bragg's law. Scanning the crystal and detector through a range of angles records the spectrum sequentially. Because the detector sees one narrow wavelength at a time, background is very low, resolution is high, and overlapping lines are separated. Detection limits reach the low parts per million or better for many elements, and light elements from beryllium or boron upward can be measured with suitable crystals, vacuum and flow detectors. Sequential instruments are flexible but slower, while simultaneous instruments with fixed crystal channels measure many elements quickly. WDXRF is standard for cement, mining, glass, metals and geological major-oxide analysis where precision and accuracy are paramount.

How does it work?

A primary X-ray beam from a tube or radioisotope source ejects inner-shell electrons from sample atoms. Electrons from higher shells fall into the vacancies and emit X-ray photons whose energies equal the difference between the two levels, which is unique to each element. The intensity of each characteristic line is proportional to the amount of that element, so calibration with reference materials gives concentration. Energy-dispersive instruments use a semiconductor detector such as silicon drift to measure photon energies directly and record the whole spectrum at once. Wavelength-dispersive instruments use analyzing crystals to diffract specific wavelengths to a detector, giving better resolution and lower detection limits, especially for light elements. Matrix effects from absorption and secondary excitation are corrected by fundamental parameters or empirical influence coefficients, and sample form is matched to calibration standards.

What are the key features?

• Analyzing crystals diffracting one wavelength at a time
• High resolution with very low background
• Low detection limits for trace elements
• Light elements from beryllium with vacuum and flow counter
• Sequential scanning or simultaneous fixed channels
• High-precision major-oxide analysis

What are the technical specifications?

A typical wavelength-dispersive x-ray fluorescence spectrometer configuration offers element range of Be or B to U, detection limit of 0.1–10 mg/kg typical, analyzing crystals of LiF, PET, Ge and others, X-ray tube power of 1–4 kW, measurement time of 1–20 min per sample and atmosphere of vacuum or helium. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Wavelength-Dispersive X-Ray Fluorescence Spectrometer is used in cement and clinker major-oxide analysis, geological and mining exploration samples, glass, ceramics and refractory materials and metals and alloy certification. Across the wider XRF class, laboratories also deploy it for elemental analysis of alloys, ceramics and glass, roHS and restricted substance screening and coating thickness and thin-film composition.

Which standards and certifications apply?

Relevant standards and methods include ASTM E1621 Wavelength dispersive X-ray fluorescence, ASTM D4294 Sulfur in petroleum products by EDXRF, ISO 3497 Metallic coatings — X-ray spectrometric thickness, IEC 62321 Determination of restricted substances in electrotechnical products, US EPA Method 6200 Field portable XRF for soil, ISO 13196 Soil quality — Screening of selected elements by EDXRF, IEC 61010-2-091 and ISO/IEC 17025. Certification candidates for this model are CE, Radiation safety enclosure and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

XRF instruments are regulated radiation devices, so installation requires shielding, interlocks, radiation surveys and trained operators, with portable units also needing safe work procedures. Sample preparation strongly affects accuracy: surface contamination, insufficient thickness and particle size effects bias results, and powders are best pressed or fused. Calibration must match the sample matrix, and drift is monitored with check standards. Vacuum or helium systems need clean seals and gas supplies for light elements. Detector windows and X-ray tubes are wear parts with finite life. Keep records of tube hours, calibration and checks, and dispose of X-ray components according to radiation regulations.

How do I select the right Wavelength-Dispersive X-Ray Fluorescence Spectrometer?

Select wavelength-dispersive XRF when precision for major elements, light-element capability or the lowest XRF detection limits are required, as in cement, mining and glass laboratories. Specify the element range, sample types and throughput. Fused beads give the best accuracy for oxides, and automatic sample changers support long production sequences.

How does it compare with other XRF variants?

Select an XRF configuration by element range, detection limit and sample type. Energy-dispersive instruments are compact, fast and well suited to routine screening and multi-element analysis, with moderate resolution. Wavelength-dispersive instruments cost more and are slower but excel for light elements, precise major-oxide analysis and low detection limits. Total reflection instruments reach ultratrace levels on small sample spots and serve semiconductor, water and biological analysis. Polarized energy-dispersive instruments lower background for trace work without the cost of wavelength dispersive optics. Micro-XRF adds spatial resolution for inclusions, coatings and forensic samples. Consider sample size, whether vacuum or helium purge is needed for light elements, automation level and the regulatory method your laboratory must follow before deciding.