Efforts are underway to optimize two-dimensional X-ray detectors, which have become a standard at synchrotron sources for practically all applications including tomography. Area detectors can be divided into two main classes: in direct detection the X-ray photons are directly converted to an electrical signal via electron-hole pair creation, either in a semiconductor or in a gas; in indirect detection the X-ray photons are first converted into visible light that is subsequently converted to an electronic signal in the semiconductor. So far, the most effective, low-cost and low-risk solution for tomography has been indirect detection, where a scintillator converter screen is optically coupled to an integrating detector, either a commercial CCD camera, or a specially developed amorphous photodiode array. This chapter explains this technology and discusses the various components. It begins with a survey of the various existing types of X-ray conversion screens. This is followed by a discussion of the optical relays and the light sensors required to convert the light into a digital image.
Keywords: two-dimensional X-ray detectors, indirect detection scintillation mechanism, spatial resolution, powder screens, crystal converter screens, optical coupling