An investigation into the use of secondary-electron signal multipliers in image iconoscopes

The limiting factor for low-light operation of the image iconoscope is the threshold set by the pre-amplifier noise. Although it has long been thought possible to overcome this limit by the use of a secondary-electron signal multiplier, no working example of such a tube has, up to the-present, been described. In the paper it is shown that by the aid of an electron transmissive screen in front of the first multiplier dynode, complete collection and sufficient acceleration of the secondary electrons leaving the target can be accomplished. Furthermore, by using a suitable geometry of the multiplier-and-target arrangement a plane field can be presented to the storage surface, achieving uniform picture generation over the entire target area. A construction is investigated where the multiplier assembly has the form of annular discs closely spaced and enclosed by a circular screening box. Results illustrating collection efficiency, correction of residual picture unevenness, etc., are presented in graphs, oscillograms and television pictures. The performance of the tube is discussed with regard to the elimination of the photo-current noise component and various improved methods of operation are indicated.