An Image Intensifier System for the Observation of Nuclear Events

An image intensifier system is described in which a two-stage tube, Mullard VX8529 is coupled by a lens to an English Electric P829, a transmission-secondary emission type of intensifier with a gain of >105. The system has a large area input cathode, 15 cms in diameter, and is intended to give a high efficiency of detection for photoelectrons originating from that cathode. It is intended that the system will be used to detect images at extremely low light levels, such as the ring image produced from a Cherenkov radiator by a lens or mirror. The experiments described concentrate on the performance of the system and its components. In particular measurements are made of the efficiency of detecting primary photoelectrons and of the accuracy in determining the position of an image. It is shown that for illumination in central regions of the photocathode~ 2.5 spots of light are photographed on the output phosphor screen for each photoelectron. Approximately 1.8 are in a region surrounding the the true image position and for a line image have a distribution with a standard deviation (referred to the input photocathode) of 2.7 mm. Of these ~0.5 are found to be bright spots in the correct image position. The remaining spots are widely distributed. Measurements have also been made of the detection efficiency for single photoelectrons with the high gain P829 alone. For the conditions of the present experiment it is found that only 30% produce a detectable signal in the correct image position.