This grease must be used to install a replacement Scintillation Crystal or Photomultiplier Tube. This silicone grease removes the air gap between the PMT and the crystal resulting in better photon transmission into the PMT.
This grease is a clear, colorless, silicone, optical coupling compound that features excellent light transmission and low evaporation and bleed at 25C. It has a specific gravity of 1.06, an Index of Refraction of 1.465 and has a very flat transmission of approximately 95% for wavelengths between 280nm and 700nm. There is a sharp fall off below 280nm. Transmission at 270 and below is about zero.