Function of X-ray fluorescence spectrometer

An XRF spectrometer identifies and quantifies elements in a sample by measuring the characteristic X-ray fluorescence emitted when the sample is irradiated with high-energy X-rays.

Fundamental Principle

X-ray fluorescence (XRF) relies on the interaction between high-energy X-rays and atoms in a sample. When a sample is exposed to X-rays, the energy can eject tightly bound inner-shell electrons, creating vacancies in the atom's electron shells. Outer-shell electrons then transition to fill these vacancies, releasing energy in the form of secondary X-rays, known as fluorescent X-rays, which are characteristic of each element. The energy of these emitted X-rays is unique to the element, allowing qualitative identification, while the intensity of the emission correlates with the element's concentration, enabling quantitative analysis .

Instrument Components

An XRF spectrometer typically consists of:

• X-ray source: Generates high-energy X-rays, often using an X-ray tube with a metal anode. Electrons accelerated at high voltage strike the anode, producing X-rays that irradiate the sample .
• Detector: Measures the energy and intensity of the emitted fluorescent X-rays. Common detectors include Silicon Drift Detectors (SDD) for energy-dispersive XRF (EDXRF) or crystal-based detectors for wavelength-dispersive XRF (WDXRF), .
• Data processing system: Converts detected X-ray energies and intensities into a spectrum, identifies elements using Moseley's law, and quantifies concentrations through calibration and matrix corrections .

Operational Steps

1. Excitation: The sample is irradiated with primary X-rays, causing inner-shell ionization.
2. Emission: Outer electrons fill the vacancies, emitting characteristic fluorescent X-rays.
3. Detection: The detector captures the emitted X-rays, recording their energies and intensities.
4. Analysis: Software processes the spectrum, identifies elements, corrects for matrix effects, and calculates concentrations .

Sample Preparation

XRF is largely non-destructive and requires minimal sample preparation. Solids can be analyzed directly or pressed into pellets, powders may be mixed with a binder, and liquids can be placed on thin films. Proper preparation ensures homogeneous exposure and accurate fluorescence measurement .

Applications

XRF spectrometers are widely used for geological analysis, metallurgy, environmental testing, quality control, and cultural heritage studies. They can detect elements from light elements like fluorine to heavy elements such as uranium, often simultaneously, with detection limits ranging from sub-ppm to 100% for major components . In summary, the working principle of XRF is based on the emission of characteristic X-rays from atoms excited by high-energy radiation, with detection and analysis providing a rapid, non-destructive method for elemental identification and quantification.