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PHOTOMULTIPLIER VALVE, 1960's
Photomultiplier tubes (photomultiplier's or PMTs for short), members of the class of vacuum tubes, and more specifically photo tubes, are extremely sensitive detectors of light in the ultraviolet, visible and near infra-red. These detectors multiply the signal produced by incident light by as much as 100 million times (i.e., 80 dB), enabling (for example) single photons to be individually detected when the incident flux of light is very low. The combination of high gain, low noise, high frequency response and large area of collection has earned photomultiplier's an essential place in nuclear and particle physics, astronomy, medical diagnostics including blood tests, medical imaging and motion picture film scanning (telecine). Semiconductor devices, particularly avalanche photo diodes, compete with them, but photomultiplier's are uniquely well-suited for applications requiring low-noise, high-sensitivity detection of light which is imperfectly collimated. While photomultiplier's are extraordinarily sensitive and moderately efficient, research is still under way to create a photon-counting light detection device that is >99% efficient; such a detector is of interest for applications related to quantum information and quantum cryptography. Elements of photomultiplier technology, integrated differently, are the basis of night vision devices.
The photomultiplier, invented in 1936, is rooted in the science of the photoelectric effect, and that of secondary emission - i.e., the ability of electrons in a vacuum tube to, by striking an electrode, cause the emission of additional electrons.
Photomultiplier's are constructed from a glass vacuum tube which houses a photo cathode, several dynodes, and an anode. Incident photons strike the photo cathode material which is present as a thin deposit on the entry window of the device, with electrons being produced as a consequence of the photoelectric effect. These electrons are directed by the focusing electrode towards the electron multiplier, where electrons are multiplied by the process of secondary emission.
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- Nov. 2012 - Sad to say that the former EMI factory in Bury St., Ruislip, is no more - it's a new housing development, of course.
.......... Colin Carroll, Langford, Beds, 13th of November 2012
- I used to work at the EMI factory in Ruislip where they made these photomultipliers. The description given is very good and obviously written by an expert. I wasn't an expert on the tubes, but worked on the test equipment used to check them. I also remember the expert glass-blowers who used to construct the envelopes and connect them to the vacuum pumps. I made many friends there in the early 70s, and joined an Am-Dram group based in Ruislip. I also met my wife-to-be who lived nearby although she didn't work at EMI. If anyone reading this is interested in getting in touch through this site I would be delighted. I still have contact with EMI at their archives in Hayes, Middx., through my present job, but the firm is very different these days. However, the factory in Ruislip is still there.
.......... Colin Carroll, Langford, Biggleswade, Beds., 27th of December 2009