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Radioscopic Testing (RS)

Radiographic testing is able to obtain an image of internal volumetric discontinuities (in some cases it is possible to detect some advantageously orientated 2D defects). The most frequent use of RT is for examination of welds, castings (also very complicated shapes), electrotechnical industry, civil engineering, ... Due to tradition and demonstrativeness of the method RT is one of the most important in NDT of the equipment with higher level of the inadvisability (e.g. pressure vessels), in the aerospace and petrochemical industry.

Suitable alternative to Radioscopy are the computed and digital radiography
Computed radiography (CR), Digital radiography (DR)

Physical background

In radioscopic method an intensifier is used for transformation of invisible radiation profile to visible image. X-ray photons drop on the input shade with the phosphor layer (crystal compound, which is able to change X-ray photons with the high energy to the photons of visible light). The input shade is in direct contact with the photocathode. Due to the dropping photons of visible light electrons are emitted from the photocathode. These are subsequently accelerated by high voltage of the anode (the voltage is usually about tens of kV) and propping on the output shade. The phosphor layer also covers the output shade, and due these visible photons are emitted. The image could be focused by interaction of electromagnetic field and electrons in the image intensifier.

Image intensifying is done by high accelerating voltage and by compression of brightness information from input shade (usually with the diameter about cca 20 cm to the output shade diameter cca 2 cm).
The original X-ray photons go through the whole radioscopic system. In order to protect the next parts of RS system it is profitable to deflect the visible light beam by the optical prism in 90° angle. After passing of optical way visible light is transferred into video signal by the CCD camera element.
The characteristic curve of the image intensifier is (as well as curve of the digital system) linear. The difference is, that RS system has expressive area of the over-saturation.

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