X-ray-sensitive vidicon tube for low-level radiation imaging

Abstract

A new type of imaging tube for x rays and γ rays in the 80-keV and higher energy range is described. The tube has the ability to image low flux levels of incident radiation by the process of charge integration in the target plate while the reading electron beam is turned off. The target plate consists of a layer of lead deposited on a substrate. The lead layer converts a portion of the incident radiation into photoelectrons. These photoelectrons travel through a low-density layer of cesium iodide deposited on the lead layer and create secondary electrons. An electric field maintained across the cesium iodide layer causes the secondary electrons to be collected by the conductive backing of the target plate, thereby leaving a charge pattern on the surface. A scanning electron beam neutralizes this charge pattern, resulting in the flow of signal current. The technique of obtaining maximum signal current for a given radiation energy is one of optimizing the thickness of the lead layer and the thickness and density of the cesium iodide layer. Experiments designed to determine the optimal values of these parameters are described. Imaging studies carried out using an x-ray machine as well as a 133Xe radioactive source are described.