ENERGY SELECTIVE IMAGING-SYSTEMS BASED ON MONOLITHIC CDZNTE ARRAYS OPERATED IN A HIGH-SPEED COUNTING MODE

The excellent inherent energy resolution of CdZnTe and the evolution o f techniques to fabricate this material into large, multi-pixel monoli thic arrays, have encouraged the development of practical, multi-funct ion, x-ray imaging systems. These systems are capable of simultaneousl y recording the x-ray image of an object while identifying the average atomic number of each of its internal components. The primary improve ment of this new sensor technology is the ability to break down the de tected radiation into energy bins after passing through the sample. Th e reduced fraction of scattered radiation recorded in a collimated, li near scanner image makes it possible to separate differing energy regi ons of the beam with a single bremsstrahlung source and a single, mult iple discriminators. Such imaging systems have immediate applications in security and contraband detection, as well as a number of specializ ed uses in medical imaging. This review covers recent work carried out at SAIC in the development of these systems including the characteriz ation of the detector devices, the requirements for the electronic rea dout system and a number of examples of images taken with prototype sy stems. Studies have been conducted with examples of both linear and ar ea 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 w ith these systems exhibit noise limits set by the available statistics and excellent point spread functions. Practical limitations in the us eful pixel resolution approach 0.1 mm with stopping thickness of sever al millimeters. This suggests that high resolution scanners with x-ray tube potentials of several hundred kilovolts are feasible with this t echnology.