Photomultiplier tube with internal light-guiding for calibration - has internal or external light source at rear of tube which illuminates photosensitive surface from front

摘要

A photosensitive surface (11) is deposited on the transparent window (13) of the photo-multiplier and the glass vessel is pumped out and sealed during fabrication leaving a sealing point (23) at the rear end of the tube. A light source (18), which can be, for preference, an electroluminescent diode is positioned close to the apex of the glass envelope. Light is transmitted by multiple internal reflection around the glass envelope and impinge on the photo sensitive surface from the frontal direction. In one of three variations provided, the apex of the tube is soldered into a metal cylinder (28) whose end is formed into a transparent plug (29), allowing the use of an external light source. Alternatively, or additionally, an internal length of optical fibre can be used to direct the light.