Filtern
Dokumenttyp
- Vortrag (2)
- Zeitschriftenartikel (1)
Sprache
- Englisch (3)
Schlagworte
- Dual-energy (3) (entfernen)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (2)
The progress in X-ray detector electronics (sensitivity and speed) allows meanwhile fast single photon detection by a matrix detector. Combined photon counting and energy discrimination is implemented in the electronic circuit of each detector pixel. The company XCounter developed detectors based on CdTe single crystals, which can be tiled to larger areas and have a pixel size of 100ìm. The largest area available in beginning of 2014 is 50x75 mm². These detectors have very promising properties, which make them very suitable for NDT applications:
1. A CdTe attenuation layer of 750 µm thickness allows efficient X-ray detection up to ca. 300 keV. In counting mode only photon noise is important; no other detector noise sources need to be considered. There is no Offset signal without radiation.
2. Each of the detector pixels has two energy thresholds. These can be used for dual energy imaging for materials separation. Also the suppression of scattered radiation by energy thresholding will improve the image contrast sensitivity. First experiments will be presented which demonstrate the advantages of this new detector technology over the conventional charge integrating detectors.
A challenge is the development of a modified detector calibration procedure, which becomes critical at longer exposure times.
Properties and application areas of photon counting and energy resolving digital detector arrays
(2015)
Since a few years the direct detection of X-ray photons into electrical signals is allowed by usage of highly absorbing photo conducting materials (e.g. CdTe) as detection layer of an underlying CMOS semiconductor X-ray detector. NDT energies up to 400 keV are today also possible. The image sharpness and absorption efficiency is improved by the replacement of the unsharp scintillation layer (as used at indirect detectors) with a photo conducting layer of much higher thickness and a high voltage across it. If the read-out speed is high enough (ca. 50 – 100 ns dead time) single X-ray photons can be counted and their energy measured. Read-out noise and dark image correction can be avoided. By definition of energy thresholds selected energy ranges of the X-ray spectrum can be detected or also suppressed. This allows material discrimination by dual-energy technique or the reduction of image contributions from scattered radiation, which results in an enhanced contrast sensitivity. To use these advantages in an effective way, a special calibration procedure has to be developed, which considers also time dependent processes in the detection layer. This contribution presents some of these new properties of direct converting DDAs in comparison to the conventional indirect converting detectors for fiber composites and thick walled steel pipes (up to 35 mm wall thickness). Possible new application areas of NDT will be discussed for material discrimination especially within fiber reinforced composites (e.g. CFRC und GFRC).
Modern wind turbine rotor blades consist of sandwich shell segments made from glass fiber reinforced polymers. During manufacturing, defects can arise which could lead to failure of the whole component under dynamic mechanical and thermal loads. Hence during operation defects can arise which, if detected, can be repaired locally and in-situ by applying repair patches instead of taking the whole rotor blade down and repair it remotely. This method is much more time and cost effective, since the shut-down time of the energy converter is limited to a minimum. These repair patches can, however, also lead to new defects if not applied optimally. Therefore, it is necessary to control the quality of the repair patches to ensure the best possible restoration of structural integrity of the component. As a rotor blade is an object with a large aspect ratio, X-ray laminography is predestined to provide 3D information of the objective volume. To enhance the amount of information gained from laminographic reconstruction, we use in this study a photon counting and energy discriminating X-ray detector and apply a material decomposition algorithm to the data. By inherently separating the incident spectra within the detection process into two distinct energy bins, the basis material decomposition can provide material resolved images. Choosing glass and epoxy resin as basis materials and numerically solving the inverse dual-energy equation system, the reconstructed laminographic datasets contain highly valuable information about the distribution of the basis materials within the structure. Furthermore, cross- artifacts arising from the limited angle of the projection data can be reduced by this method which allows to investigate structures that were hidden underneath the artefacts.