XRF (X-ray fluorescence) is a non-destructive analytical technique used to determine the elemental composition of materials. XRF analyzers determine the chemistry of a sample by measuring the fluorescent (or secondary) X-ray emitted from a sample when it is excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays (“a fingerprint”) that is unique for that specific element, which is why XRF spectroscopy is an excellent technology for qualitative and quantitative analysis of material composition.
The X-ray fluorescence process
- A solid or a liquid sample is irradiated with high energy X-rays from a controlled X-ray tube.
- When an atom in the sample is struck with an X-ray of sufficient energy (greater than the atom’s K or L shell binding energy), an electron from one of the atom’s inner orbital shells is dislodged.
- The atom regains stability, filling the vacancy left in the inner orbital shell with an electron from one of the atom’s higher energy orbital shells.
- The electron drops to the lower energy state by releasing a fluorescent X-ray. The energy of this X-ray is equal to the specific difference in energy between two quantum states of the electron. The measurement of this energy is the basis of XRF analysis.
Interpretation of XRF spectra
Most atoms have several electron orbitals (K shell, L shell, M shell, for example). When x-ray energy causes electrons to transfer in and out of these shell levels, XRF peaks with varying intensities are created and will be present in the spectrum, a graphical representation of X-ray intensity peaks as a function of energy peaks. The peak energy identifies the element, and the peak height/intensity is generally indicative of its concentration.
Energy dispersive X-ray fluorescence (EDXRF)
EDXRF is the technology commonly used in portable analyzers. EDXRF is designed to analyze groups of elements simultaneously in order to rapidly determine those elements present in the sample and their relative concentrations—in other words, the elemental chemistry of the sample.
To understand how this information can be used, consider scrap metal. Recyclers need to positively identify numerous alloy grades, rapidly analyze their chemical composition at material transfer points, and guarantee the quality of their product to their customers. Metal alloys are designed for specific functions that are not interchangeable; small variations in composition can result in significantly different mechanical properties. Luckily, handheld XRF analyzers can easily separate these grades.