Energy selective imaging systems based on monolithic CdZnTe arrays operated in a high speed counting mode

Abstract

The excellent inherent energy resolution of CdZnTe and the evolution of techniques to fabricate this material into large, multi-pixel monolithic arrays, have encouraged the development of practical, multi-function, x-ray imaging systems. These systems are capable of simultaneously recording the x-ray image of an object while identifying the average atomic number of each of its internal components. The primary improvement of this new sensor technology is the ability to break down the detected radiation into energy bins after passing through the sample. The reduced fraction of scattered radiation recorded in a collimated, linear scanner image makes it possible to separate differing energy regions of the beam with a single bremsstrahlung source and a single, multiple discriminators. Such imaging systems have immediate applications in security and contraband detection, as well as a number of specialized uses in medical imaging. This review covers recent work carried out at SAIC in the development of these systems including the characterization of the detector devices, the requirements for the electronic readout system and a number of examples of images taken with prototype systems. Studies have been conducted with examples of both linear and area arrays using relatively simple processing electronics. Problems of incomplete charge collection and energy separation are discussed along with potential solutions to these issues. Imaging measurements made with these systems exhibit noise limits set by the available statistics and excellent point spread functions. Practical limitations in the useful pixel resolution approach 0.1 mm with stopping thickness of several millimeters. This suggests that high resolution scanners with x-ray tube potentials of several hundred kilovolts are feasible with this technology.