XRF-BS Model

Technical specifications

X-Ray Back Scattering is a well-known underlying phenomenon to the X-Ray Fluorescence.

The combined analysis of the two phenomena is at the basis of the SGM proprietary XRF-BS sorter and offers a more accurate and extended analysis for sorting different metals from each other including aluminum alloys.

Fluorescence

The Fluorescence is the physical phenomenon by which an atom emits a photon when struck by a high energy photon provided by a specific X-Ray source. The emitted photon is called fluorescence photon and its energy level is specific to every chemical element and can be seen as its chemical signature.

The X-Ray Fluorescence separation technology consists in the spectrographic analysis (intensity/energy) of the distribution of the fluorescence photons emitted by a material and captured by some XRF sensors called SDD (Silicon Drift Detectors) during a certain time frame called acquisition time (3-5 milli-seconds).

Traditional XRF sorters work only on the identification of heavy metals as those chemical elements are characterized by fluorescence photons with levels of energy that are high enough to be sensed by the SDD. This is not the case with light metals (Al, Si,…) for which the energy of the fluorescence photons is too low to be sensed from a distance by the SDD.

XRF spectrographic analysis displays peaks indicating concentrations (high intensities) of photons of some specific energies characterizing the presence and concentration of some specific heavy metals or heavy metals alloys.

Back Scattering

The X-Ray Back Scattering phenomenon is an underlying phenomenon to the fluorescence and is generally considered a fallasy in the XRF spectrographic sorting analysis as, instead of being represented by a few high intensity peaks of specific energies, it is characterized by a continuous distribution of low intensity photons. Standard XRF spectrographic sorting analysis filters Back Scattering information by disregarding signals below a certain intensity.

XRF Back Scattering signals are also specific to the chemical composition of the material analyzed and, the combination of the peak analysis provided by the XRF together with the specific profiles of the continuous low energy signals provided by the Back Scattering, allow for a more accurate identification of heavy metals from each other but also for the sorting of the different aluminum alloys series from each other.

What XRF-BS does

Sorting of Scrap Aluminum in different alloy series including 5000 from 6000.
Advantages of the SGM XRF-BS versus the LIBS (Laser Induced Breakdown Spectroscopy):

• Better performing in case of critical material surfaces (painting, dirt, …). Even though the XRF-BS technology is also a surface analyser, it interacts deeper (hundreds of microns) into the material than LIBS (tens of microns).
• Greater accuracy as XRF-BS performs a continuous analysis vs LIBS which performs a spot (nano seconds) sampling micro analysis. The LIBS discontinuous analysis can be sufficient on clean, chemically homogeneous pieces like production tailings but scrap material is different, more various and therefore more demanding.
• Contrary to LIBS, the continuity of the XRF-BS analysis and the absence of focal length constraint make it independent of the shape of the piece.
• The LIBS analysis suffers from the possible presence of humidity on the material while XRF-BS is independent of it.
• Deeper analysis making it better performing in case of critical material surfaces (painting, dirt, etc).
• Continuous analysis allows for higher accuracy vs LIBS discontinuous spot micro analysis.
• Continuous analysis making it independent from the shape of pieces.
• Capacity on aluminum scrap: fraction 30 mm – 120 mm/1 ¼” – 5”: > 2 ton per hour and per module.