X-ray Fluorescence (XRF)
X-ray Fluorescence (XRF) Technology is a well-accepted method to achieve non-destructive, simultaneous elemental analysis of various types of samples. Portable Analytical Solutions (PAS) are proud to offer the Thermo Scientific Niton Analyser range of portable and hand-held Energy Dispersive X-ray Fluorescence (EDXRF) Spectrometers.
The following technical explanation can also be found on the Niton Website.
Sample Analysis via EDXRF
Hand-held Thermo Scientific Niton EDXRF Analysers, commonly known as XRF analysers, are able to quickly and non-destructively determine the elemental composition of:
- Metal and precious metal samples
- Rocks and soil
- Slurries and liquid samples
- Painted surfaces, including wood, concrete, plaster, drywall and other building materials
- Dust collected on wipe samples
- Airborne heavy elements collected on filters
Thirty or more elements may be analysed simultaneously by measuring the characteristic fluorescence x-rays emitted by a sample. Thermo Scientific Niton hand-held XRF analysers can quantify elements ranging from magnesium (element 12) through uranium (element 92), measuring x-ray energies from 1.25 keV up to 85 keV in the case of Pb k-shell fluorescent x-rays excited with a 109Cd isotope. These instruments also measure the elastic (Raleigh) and inelastic (Compton) scatter x-rays emitted by the sample during each measurement to determine, among other things, the approximate density and percentage of the light elements in the sample.
How does EDXRF work? Each of the elements present in a sample produces a unique set of characteristic x-rays that is a “fingerprint” for that specific element. EDXRF analysers determine the chemistry of a sample by measuring the spectrum of the characteristic x-rays emitted by the different elements in the sample when it is illuminated by x-rays. These x-rays are emitted either from a miniaturised x-ray tube, or from a small sealed capsule of radioactive material.
A fluorescent x-ray is created when an x-ray of sufficient energy strikes an atom in the sample, dislodging an electron from one of the atom’s inner orbital shells. 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, and the energy of this x-ray is equal to the specific difference in energy between two quantum states of the electron.
When a sample is measured using XRF, each element present in the sample emits its own unique fluorescent x-ray energy spectrum. By simultaneously measuring the fluorescent x-rays emitted by the different elements in the sample, hand-held Thermo Scientific Niton XRF analysers rapidly determine those elements present in the sample and their relative concentrations â€“ in other words, the elemental chemistry of the sample. For samples with known ranges of chemical composition, such as common grades of metal alloys, these XRF â€˜guns’ also identify most sample types by name, typically in seconds.
Light Element Analysis
Metal Sample Fluorescence
Recent advancements in Geometrically Optimised Large area Drift Detector (GOLDDâ„¢) technology have improved the performance of Niton hand-held XRF analysers in general, but most especially the performance on elements below atomic #17 (Mg, Al, Si, P, S, Cl). The NitonÂ® XL2t and the Niton XL3t with GOLDD technology can now detect elements as low as Mg (#12) without the use of Helium purging or vacuum pumps. However, a few applications require the very best in light element sensitivity; this analysis is best performed either with a helium gas purge or in a vacuum chamber in a laboratory environment. As the use of a vacuum with portable XRF is highly impractical (even minor punctures to the thin window used to seal the instrument from the environment will draw dust, debris and metal filings into the instrument), then a He purge unit is the most appropriate solution for the very best performance on light element analysis (Mg, Al, Si, P, S, Cl).
Niton analyser sample analysis techniques
Hand-held Thermo Scientific Niton XRF analysers automatically compensate for any external or environmental factors which may otherwise bias or distort sample analyses. These effects include:
- Geometric effects caused by the sample’s shape, surface texture, thickness and density
- Spectral interferences
- Sample matrix effects including critical absorption of the characteristic x-rays of one element by other elements in the sample, and secondary and tertiary x-ray excitation of one or more elements by other elements in the sample.
By automatically adjusting for these effects, Thermo Scientific Niton hand-held XRF analysers are able to determine the chemistries of samples of widely different compositions, typically in seconds, without any requirement for instrument users to input empirical, sample specific calibrations. In typical samples containing many elements, the elements may range in concentrations from high precent levels down to parts per million (ppm).
In sample matrices such as typical mining samples, metal and precious metal alloys, it is necessary to measure both lighter elements that emit lower energy x-rays (that are easily absorbed) as well as heavier elements that emit much higher energy x-rays (that penetrate comparatively long distances through the sample).
Thermo Scientific Niton Analysers and X-ray Fluorescence (XRF)
Compensation must be made for a variety of geometric effects. In these multi-element samples, it is also possible that one or more elements present, act as critical absorbers. The effects of absorption, enhancement and secondary fluorescence vary widely depending on the chemistry of the sample matrix, but in a sample with many elements in substantial concentrations, multiple absorptions, secondary and also tertiary XRF effects are typically present.
Thermo Scientific Niton hand-held XRF analysers compensate for all of these effects in order to determine the actual concentration of elements in multi-element samples from the modified fluorescence x-ray spectrum that these samples produce in the XRF analyser. To do this, we employ multiple methods to determine the true composition of these complex samples from their x-ray spectra. These include:
- Fundamental Parameters (FP) analysis
- Compton Normalization (CN)
- Spectral matching (“fingerprint”) empirical calibrations
- User-definable empirical calibrations
- Various combinations of these techniques.