This grease must be used to install a replacement Scintillation Crystal or Photomultiplier Tube. This silicone grease removes the air gap between the Photomultiplier Tube 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.