XRF analysis is a non-destructive technique that takes advantage of the interaction between primary X-rays and material. X ray is also called Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it on November 8, 1895. The name X was given because at the time of its discovery nothing was known about this physics phenomenon.

All material is made of atoms, in the middle of each atom is a nucleus that is positively charged due to the presence of protons and neutrons (no charge). Negatively charged electrons revolve around the nucleus in quanta called shells such as in an onion.

Their total negative charge compensated the positive charge of the nucleus, making the atom neutral. This can be changed by introducing external energy, such as X-rays. X-rays are light waves with very short wavelengths, with very high energy, which are absorbed as they pass through material, depending on the composition and density of that material.

When an atom is hit by an X-ray of sufficient energy (which exceeds the atom's binding energy), an electron in its inner orbital shells is ejected, creating vacancies. An electron from a higher atomic orbit will fall down to the vacancy in this lower energy state. This develops an emission of energy in the form of fluorescence or secondary X-rays, which is equal to the specific difference in energy between the two quantum states of the electron.

Secondary X-rays are characteristic of individual elements in the periodic table. When a sample is analysed via XRF, each element present emits these unique X-ray signals in the form of a spectrum. Also referred to as an elementary fingerprint, this spectrum is central to the performance of both EDXRF (Energy Dispersive XRF) and WDXRF (Wavelength dispersive XRF).

In EDXRF analysis, the characteristic X-rays of different elements present in a measurement are separated into a full fluorescence energy spectrum using direct excitation or indirect excitation. EDXRF technology is designed to simultaneously process whole groups of elements for qualitative or quantitative analysis and can be used in portable (geologists in prospecting) and laboratory formats.

EDXRF in itself is the solutions in different disciplines as varied such as metal and alloy production, petrochemistry, forensics, mineralogy, food analysis, environmental analysis and much more. Precious metals and gemstones are also accurately analysed with this.

X-rays are a type of electromagnetic wave similar to visible light, but with an extremely short wavelength. Compared to normal electromagnetic waves, X-rays pass easily through material and become stronger as the atomic number of the material they pass through decreases. X-ray fluorescence analysis is a method that uses characteristic X-rays (fluorescent X-rays) generated when X-rays irradiate an object.

These fluorescent X-rays possess energies characteristic of each type of element, allowing for qualitative analysis using Moseley's law and quantitative analysis using the intensity (number of photons) of each X-ray energy.

X-ray fluorescence analysis can be thought of as spectrochemical analysis within an X-ray region. It has the same characteristics as atomic absorption spectrometry and optical emission spectrometry, except that the sample does not need to be dissolved in a solution to be analysed or in a plasma flame of 6000° to 9000°C.

This makes XRF very interesting for the analysis of gold jewellery, it is not destructive. In classical gold analysis, different types of acids are used. An onyx plate is used on which the jewel is rubbed, this results in a stripe on which a drop of liquid is applied; aqua regia.

Royal water is the liquid where gold can be tested for authenticity and content. It is a mixture of hydrochloric acid and nitric acid. It is therefore very poisonous and corrosive. It is therefore necessary to proceed with caution when working with aqua regia. Gold dissolves in aqua regia and by mixing the right proportions of hydrochloric acid and nitric acid one can use the aqua regia determine the content of a particular gold object. Aqua regia is available in different compositions to test gold objects for authenticity and content (carat gold). This method has been used for hundreds of years by traders, buyers, jewellers and goldsmiths to test gold jewellery for authenticity and quality in: 8 carat gold, 14 carat gold, 18 carat gold and 21.6 carat gold.

With valuable jewellery, this system is destructive (slight damage), with XRF there is no damage and you also get the other metals that were processed outside the gold content.

There is also an electronic gold detector, Mizar, where the jewel is partially immersed in a liquid and where the content of the jewel is measured electrically.

But XRF certainly remains the best method for jewellery and for the identification of some gemstones.

For those who do appraisal on all possible metal alloys, XRF is a very good solution, scientific analysis, user-friendly and portable (1.7 kg).

Eddy Vleeschdrager, SBD Member