Survey of two-dimensional electro-optical X-ray detectors

Abstract

Electro-optical devices offer a flexible and modular approach to quantitative imaging X-ray detection. Such a detector typically consists of an energy converter coupled to a gain element which is followed by a readout device. This may, for example, be configured by coupling a scintillating screen to an image intensifier which is read by a TV camera. The large variety of commercially available energy converters, gain elements, and readout devices serve to limit the design problem to one of selecting the components, coupling them together and designing the appropriate electronics and software. The design criteria follow most directly from the nature of the particular X-ray detection problem being considered which, in turn, dictates which of two general modes the detector shall be operated in. In the photon counting mode, the gain element is of sufficient magnitude that each absorbed X-ray transmits a large and clearly recognizable signal to the readout device. This signal is real-time detected and allocated to memory. This has the advantages of high spatial resolution and high noise immunity; it has the disadvantage of a low maximum count rate. In another mode, termed the analog mode, the gain element is adjusted so that an individual x-ray makes a contribution comparable with the per-picture element readout noise on a readout device capable of integrating the signal from many X-rays. The magnitude of the integrated signal corresponds to the number of quanta incident. Since X-rays are not individually processed extremely high count rates can be accommodated. The primary disadvantages here is that the readout time lowers the device duty cycle. Hybrid modes are possible. The survey will emphasize the characteristics and principal limitations of the available components as applied toward synchrotron X-ray detection. Methods of coupling the components and modes of reading the final signal will be discussed. The literature pertaining to electro-optical devices that have been constructed will be briefly surveyed. Finally, the need for particular avenues of research and development will be outlined.