X-Ray Noise Observation Using a Photoconductive Pickup Tube

Abstract

A television pickup tube arrangement using a Vidicon for the direct recording of x‐ray images is described. The transmitted x‐ray picture shows noise characteristics that are clearly those of the absorbed x‐ray photons. The internal conversion gain (number of carriers generated per absorbed x‐ray photon) is estimated by two independent methods, one of which is based on a measurement of x‐ray noise. Both methods give a gain of about 500 for a 100 kv x‐ray photon. The agreement between the two methods is evidence for the validity of the simple electron‐multiplier model for the noise current in the photoconductive selenium target. The appearance of x‐ray noise means that all the information contained in the absorbed fraction of the x‐ray beam is being transmitted. Thirty pictures per second are transmitted when irradiating the Vidicon with a 5 ma, 100 kv x‐ray beam at a distance of two feet. Wires of one mil diameter were clearly observable.