What are X-rays?

X-rays are photons similar to light but with higher energy. They are produced by accelerating electrons which then strike a target. Removing electrical power stops any X-rays being produced. X-rays are attenuated (or absorbed) in different ways depending on the energy and the type of material it is passing through. Higher density materials, with more atoms in the material, will absorb more than low density materials.


Quantitative Dual-energy X-ray Absorptiometry (qDXA)

qDXA uses two X-ray beams, each with a different energy, and two high resolution detectors, to measure the amount of photons absorbed in the organic material. The software can then measure the amount (quantity) of the selected atoms – usually oxygen and carbon. As the material moves under the scanner clever algorithms calculate various physical parameters such as weight, moisture, energy value etc.

In addition, the technology also provides for a visual picture (like a normal X-ray image) which allows us to identify material with higher densities –  usually debris such as metal and plastic.

The scanners are calibrated and verified against accepted measurement techniques such as the gravimetric (oven) method.

From theory to practice

Each measurement application is determined on an atomic level. The amount of attenuation of a beam of X-rays depends on the type of atom, how closely packed the atoms are, and the thickness of the material. The key elements in a material are identified and suitable X-ray energies and intensities selected. The amount of attenuation of the X-rays due to these different elements is measured and algorithms used to calculate the weight or moisture content. Corrections are made for the material holder and the readings calibrated against trusted reference methods.

The data is calculated for each pixel on the detector to form a 2-dimensional map. Here image analysis can be used to measure the surface area of foreign objects and determine if an alarm should be triggered.


Organic material properties

All organic material contains Oxygen and Carbon atoms with sufficient density to record the attenuation of X-rays. The material is analysed in the laboratory to determine the amount of Oxygen atoms bound within the material. The amount of attenuation of the high energy and the low energy beams is then run through several algorithms to tell us about the material composition. Attenuation due to other elements can be measured by changing the energy according to the application requirements.

Inorganic material has much higher attenuation withe very little signal reaching the detector. This shows up clearly when the pixels are arranged to make a two dimensional image.