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The 9531KA is a magnificent photomultiplier that has 11 stages of amplification and a large collection window.
R J Sutherland has supplied the attached data sheet and makes the following comments.
The 1970 data sheet says 'The EMI type 9531 is a unique design in which the front end geometry has been carefully optimised in order to give the best resolution with 75 mm scintillation crystals. It should be noted, for the benefit of present users, that the focus element has been eliminated, resulting in a marked improvement in (energy) resolution. Standard 75 mm photomultipliers have cathode diameters of only 65 mm, whereas the 9531 has very closely a 75 mm diameter cathode making a very good match with 75 mm scintillators. The 9531 series have 11 CsSb venetian-blind dynodes.' The standard photocathode type was S11.
This exhibit is slightly unusual. The 'A' suffix indicates a tube produced to customer's specification, and the 'K' suffix indicates a tube produced with an added plastic (diheptal) sprung-pin base rather than the usual glass-only hard-pin base. But this exhibit doesn't quite have either, but looks very much as if it may at one time have had a plastic base which was subsequently removed. The data sheet doesn't show a -K base option for this tube, but that may have been the nature of the custom spec.
Incidentally, flying-lead versions of some PMTs were also produced, but they were given the -F suffix instead..
The insert picture shows the photocathode. In use the dynodes are connected to increasing positive voltages, and the maximum potential is applied to the anode, from where the output signal is collected. A photomultiplier this large was probably used for detecting single events in basic scientific research.
The end window envelope is 85 mm in diameter at the window and reduces to 47 mm diameter along the multiplier chain, and excluding the special base pins, is 150 mm tall.
References: Data-sheet & R J Sutherland.


Absolute Maximum Operating Conditions
Electron Multipliers
PDF scanned from an original document held by the museum
Updated October 21, 2012.
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