X Ray Image Sensors Using A Photoconductor And An Optical Adressing Or Read Out Technique.

ABSTRACT. The different image sensors using a photoconductor as X ray to electric charges converter and optical techniques for image adressing or read out are reviewed, with a special attention to x ray photoconductor. 1. BASIC PRINCIPLES. The photoconductor may be used with one or two transparent Blocking Electrodes (BE) and subjected during recording to a constant voltage ; therefore, the image is recorded as spatial space charge distribution at the interface(s) photoconductor / dielectric. An other possibility consists in recording the space charge in the bulk of the photoconductor, in which photocarriers traps are provided in the bandgap. In that case, transparent Ohmic Electrodes (OE) are deposited on the photoconductor ; the electric field may be parallel to the light beam (longitudinal configuration OEL) or perpendicular (Transverse configuration GET). In the dark, under short circuit conditions, the storage time of the recorded latent image is in first approximation equal to the dielectric relaxation time of the structure. Optical read out of the latent image can be performed following two techniques. First, the electrodes can be connected to a charge amplifier, which output modulates the Wehnelt of a CRT ; a light beam is deflected 139