PMT's

The Photomultiplier Tubes and Structure

The photomultiplier tubes (PMTs) are the eyes of the detector. PMTs are very sensitive light detectors, capable of sensing single light photons and producing an electrical pulse that travels to the data acquisition electronics.

The PMTs consist of high voltage dynode plates within an 8" glass bulb. Light photons interact with a thin film on the inside of the glass to eject an electron. This electron is accelerated towards the high voltage plates where it causes a cascade of electrons to produce the pulse. SNO has 10,000 of these PMTs so that we can collect as many of the photons as possible from the Cherenkov light that results from the neutrino reactions.




		The PMTs are housed within ABS plastic "hex cells" which are bolted together into panels.



	Due to the sensitivity of the detector the PMTs had to be of the highest quality, both in terms of performance and cleanliness. The glass bulbs were blown in Germany from special UV-transparent, low-radioactivity glass, then shipped to Japan to have the high voltage dynodes installed.


	The 10,000 photomultipliers (PMTs) in SNO must be held in place on an 18 meter sphere surrounding the heavy water vessel. The PMT support structure was engineered and built by scientists from Lawrence Berkeley National Laboratory (California). This support structure must be very strong and manufactured from a special grade of clean stainless steel to prevent contamination of the water.




	Andrea T. Hughes - March 2004


	The photomultipier tube support structure.


	The photomultipier tube support structure installed inside the mine.


	[Home] [Neutrino's] [Cosmic Rays] [Reactions] [Results] [References]