Bicron does offer a special silicone goo for scintillator to PMT interface at a scandalous price (I forget the exact figure, but it's on the order of $50-100 for a few cc's worth, maybe more). What you have to figure is that this fluid will be good for just about every application, from photon counting to whatever (well, it'd better be, at that price...), and over a very wide range of wavelengths. We are looking at a narrow range in the visible, with relatively large pulse height. I would suspect that the turbidity of the silicone grease in a very thin layer is more than compensated by the gain from the index matching between the scintillator and the PMT glass. Otherwise,since you have an imperfect interface, you can have two air to dielectric interfaces, with consequent reflection losses.
The caveat about cloudiness does not apply to Dow Corning DC-200, which is clear. This material is specifically mentioned for scintillator to PMT index matching in William Price's book on radiation detection circa 1964. It is also mentioned in another reference as a good candidate for a high voltage insulating oil (if you have deep pockets). I was lucky enough to pick up a small can of the stuff at a surplus store. Maybe it's not all that hard to find if you ask around. I can't imagine it's anywhere near as expensive as the stuff Bicron sells, especially if it's being touted as an insulating oil.
Created on Monday, April 16, 2001 10:46 PM EDT by Richard L. Hester