The RCA 931 PMT is the one of the first PMTs ever designed and it is one of the slowest and has the lowest gain. It has a rounded glass end and a tubular body. It has a standard 8 pin octal base, but with 12 pins, and looks like an old fashioned radio tube. There is no way to couple a scintillator to it. They are still available from Newark electronics for $115.83 or from most any hamfest, NOS for $1.00. There main application was in countless thousands of absorption and transmission spectrophotometers/absorption meters of the 50-80's era.
Their gain was super low, for a PMT, and the light entered all along the cylindrical side of the tube. There was no photocathode evaporated onto the tube glass at all.
For our purposes, having a 931 is like have nothing at all. That's why I said I bet those folks have a pile of 'em used as tradeins. Not so much because what they have is a replacement for the ancient PMT, but because there are so many of them lying around as un-usable NOS tubes. It would be like they are giving away their modern solid state sensors for trash. Of course the tiny diameter item they offer is probably pretty close to worthless itself, so far as most serious nuclear detection applications are concerned.
Richard Hull
Created on Friday, January 26, 2001 9:38 AM EDT by Richard Hull