XRF Principle

What is X-ray fluorescence?

X-ray fluorescence is a non-destructive analytical technique that identifies and quantifies the elements present in a sample by measuring the characteristic X-rays they emit. Because almost every element from sodium to uranium has its own unique X-ray “fingerprint”, a single measurement can report the full elemental composition of metals, powders, liquids, plastics and geological materials without dissolving or destroying the sample.

XRF spectrometers are used wherever composition matters: verifying alloy grades, screening precious metals, checking coating thickness, monitoring environmental contaminants and controlling incoming raw materials.

The physics: excitation and emission

Every atom is built from a nucleus surrounded by electrons arranged in shells (K, L, M …) at fixed energy levels. When a primary X-ray from the instrument's tube carries enough energy, it ejects an electron from one of the inner shells, leaving a vacancy and an unstable atom.

The atom stabilises almost instantly: an electron from a higher shell drops down to fill the vacancy, and the surplus energy is released as a secondary — or “fluorescent” — X-ray. The energy of that fluorescent X-ray equals the difference between the two shell energies, and because those energies are unique to each element, the emitted energy tells you exactly which element produced it.

From counts to concentration

An energy-dispersive (ED-XRF) detector records every fluorescent photon and sorts it by energy, building a spectrum of peaks. The position of a peak identifies the element; the number of photons under the peak — its intensity — is proportional to how much of that element is present.

Converting intensity into concentration relies on calibration against known reference standards and on correction for matrix effects, where the surrounding elements absorb or enhance one another's signals. Modern software applies these fundamental-parameter and empirical corrections automatically to deliver quantitative results in seconds.

• Non-destructive — the sample is unchanged and can be re-tested
• Simultaneous multi-element analysis, Na (11) to U (92)
• Minimal sample preparation for solids, powders and liquids
• Fast: qualitative screening in seconds, quantitative results in minutes
• Wide dynamic range, from trace ppm levels to major percentages

Sample preparation still matters

XRF only “sees” the surface layers a few micrometres to millimetres deep, so a representative, homogeneous and flat presentation is essential for accurate results. Metals are ground or machined flat, powders are pressed into pellets or fused into glass beads, and liquids are measured in cups with a supporting film.

Matching the physical form and particle size of samples and standards removes a common source of error and makes results repeatable and defensible.

Choosing the right XRF instrument

SPECTRO's ED-XRF range covers benchtop analysers such as the SPECTRO XEPOS and SPECTROCUBE for laboratory precision, the SPECTRO MIDEX for small-spot and mapping work, and handheld SPECTRO xSORT analysers for point-and-shoot use in the field. As the authorised SPECTRO distributor in India, Nucleus helps you match the instrument to your material, elements of interest and throughput.