Within an European program we are currently developing an 85 mm, one stage proximity focused image intensifier designed for inspection of corrosion in pipes with high energy gamma sources. The tube includes a thick Csl input screen in order to get a good absorption at high energies. It is part of a portable robot system designed for crawling along the pipe while imaging. First tube prototypes have been built with the following characteristics:

• Compact design: The tube itself has an overall thickness of about 4 cm which limits the total thickness of the imaging unit (optics and CCD) to less than 15cm.
• Thick Csl scintillator input screen: 2 mm thick (4mm possible) which enables an absorption efficiency at least five times higher than in a standard Image Intensifier.
• Good resolution due to the needle structure of the Csl layer.
• No distortion, neither geometrical neither due to magnetic fields, thanks to proximity focusing. The non sensitivity of the tube to magnetic fields enables software enhancement of the images such as flat field correction.

On the basis of the same tube structure, lower energy versions are currently under development. These versions include specific Csl input screen to combine high limiting resolution (up to 7 lp/mm) and high X-ray absorption at lower energy . Different tube structures based on different Csl thickness are therefore possible to optimize X-ray absorption to a specific X-ray spectrum.

This work was supported by the European Commission Brite Euram under contract BPTR-CT95-0096 and is not subject to copyright.