Radiographic flat panel detector
These detectors permit to realize Digital radiography of objects. Radiographic Flat Panel Detectors are classified in two main categories:
1 - Indirect FPDs The most common structure of such detectors combines an amorphous silicon (a-Si) photodiodes layer coupled with a scintillator in the detector’s upper face, which is made from gadolinium oxysulfide (Gd2O2S) for low energy X-rays or caesium iodide (CsI) for high energy X-rays, gamma rays or accelerator radiation. Such scintillators convert ionising radiation to light. The emitted light is channeled through the a-Si photodiode layer where it is converted to a digital output signal. The digital signal is then read out by thin film transistors (TFT) or fiber-coupled CCDs. The image data file is sent to a computer for display & eventually image processing.
2 - Direct FPDs Amorphous selenium (a-Se) FPDs are known as “direct” detectors because X-rays are converted directly into charge. The outer layer of the flat panel in this design is typically a high-voltage bias electrode. X-rays create electron-hole pairs in a-Se, and the transit of these electrons and holes depends on the potential of the bias voltage charge. As the holes are replaced with electrons, the resultant charge pattern in the selenium layer is read out by a TFT array, active matrix array, electrometer probes or microplasma line addressing. The, the image data file is sent to a computer for display & eventually image processing. The use of these detectors is presently increasing in the cultural heritage field.
Flat Panel Detectors; FPD; Digital Detector Arrays; DDA: Solid state radiographic detectors; detecteurs radiographiques digitaux (Fr.)
Resources and Citations
- R.H.Bossi, F. Iddings, G.C. Wheeler, P.O. Moore, Nondestructive testing handbook, vol 4, Radiographic testing, 3rd edition, Columbus OH, ASNT, (2002)